Are Crystals Alive?

Here is a paper I wrote in October of 2018 examining the question: “Are crystals living things?” This seemingly simple question bifurcates into an inconclusive study of the many definitions of life and an intriguing comparison of crystals to living things based off of these definitions. What do you think; are crystals alive? Comment down below or in the forum, and feel free to be as intuitive and/or scientific as you want!

Abram Leyzorek

15 October 2017

Analysis of the Shared Characteristics Between Crystals and Living Things and Study on Definitions of life

Definitions for “life”

Life is defined differently in dictionaries (1) (7), by different scientific fields addressing the subject (2) (3), and by individual scientists studying those fields (9) (10). Entities such as viruses and self replicating proteins fuel a debate concerning whether or not they should be classified as alive or dead. In addition they also provide gray areas, blurring many definitions of life and spawning new ones (2). One conventional and well accepted definition for life requires:

  1. Cellular composition.
  2. Capacity for metabolism.
  3. Capacity for growth and development.
  4. Capacity to reproduce.
  5. Capacity to pass on individual characteristics to offspring through DNA: Heredity.
  6. Tends toward homeostasis.
  7. Capacity to respond to stimuli.
  8. The capacity for adaptation through evolution.

A definition similar to this can be found in many textbooks on biology (4). It will be referred to in this paper as the textbook definition. The aforementioned dictionary definitions (1) (7) will not feature in this paper, as their content and more is provided by the textbook definition and, therefore, reviewing them seems irrelevant to the following purpose: This paper explores whether or not crystals can be considered living under the above definition and others, first by scrutinizing crystals under the textbook definition criteria and then under other definitions. This paper then speculates about the definitions of life and why they are important or not.

Do crystals have cells?

A crystal is defined as a grouping of atoms or molecules arranged in an ordered, repeating pattern. The specific patterns are known as crystal lattices and are defined by the geometric structure of their unit cell. A unit cell is the basic structure that is repeated to form a crystal lattice (5). All crystals must maintain a charge balance; an equal amount of positive and negative charge. Crystals whose external boundaries are described by well developed faces are known as euhedral. However, not all crystal possess this feature. Additionally, crystals may not maintain their structures under changing conditions such as increased or decreased temperature, pressure, etc, but rather will assume different forms, called polymorphs, under certain conditions, while maintaining original elemental composition (6). These characteristics of crystals may demonstrate that they can be defined as living.

1. The structural, functional and biological unit of all organisms.

2. An autonomous self-replicating unit that may exist as functional independent unit of life (as in the case of unicelluar organisms), or as sub-unit in a multicelluar organism (such as in plants and animals) that is specialized into carrying out particular functions towards the cause of the organisms as a whole.

3. A membrane bound structure containing biomolecules such as nucleic acids and polysaccharides.

Definition number one is the most general and will be considered first. Different domains of living creatures have cells organized different ways, i.e. prokaryotic, eukaryotic, and archaeic (11), and have different although similar functions and composition. The same is true even at the taxonomic level of kingdom, e.g. plant cells vs. animal cells (12). If science were to accept another general classification of living creatures, e.g. crystals, it might find that that kingdom also differed in its cellular structure.

The definition of a crystal, as provided above, includes that crystals are made up of cells. They are called unit cells and are the basic building blocks of crystals. They make up the crystal lattice, the structural component. They control the functional aspects of crystals by having interstices, vacancies, and other “defects” that shape the physical properties of crystals and control the movement of atoms in and on crystals. They do this by a process where atoms move from areas of higher atomic concentration to lower atomic concentration called solid state diffusion (13). This process also controls the uptake of elements and compounds into solid solution (15). Since crystals are composed of one of the seven types of unit cells (16), their functioning on a “cellular” level is determined by their unit cells. Unit cells are the basic unit of crystalline solids, so, granted crystals are alive, unit cells are biological units. Thus the first definition of a cell can be satisfied.

In the second definition, the word “autonomous” is used. It is, of course, defined in the biological sense of the word. In that sense, it simply means having an independent existence and governing laws (17). Certainly a unit cell satisfies this definition.

The second term in definition number two is “self-sustaining.” Now, as an article by Astrobiology Magazine entitled, “Defining Life”, (18) points out, no organism can survive by itself; all life needs access to free energy and materials. So, it seems that “self sustaining” must mean that the organism can gather the energy needed to survive from some necessary materials, if they are available. Could a human, for example, self-sustain itself in space? Of course not; the proper environment in which a human could survive is not provided in space. One would not stretch logic to say that every organism needs a specialized environment to survive with proper temperature, weather conditions, food supply, etc. For a crystal to form, it needs its constituent elements close at hand. One example of a favorable environment for a crystal is a solution supersaturated with its constituent element(s). In this environment, crystals will form via nucleation (19) and will impose their structural template onto free atoms of their constituent element and organize them into more crystals (20).

The stipulations of the second definition have all been covered save one: the requirement for cells to be “specialized.” The biological definition for this term is to be set apart for a particular function (21). There are several types of defects in crystals that can enhance certain ones of their functions (13). These “defective” unit cells are set apart from the others and perform a different function; arguably, they are specialized.

At the tertiary definition of a biological cell comes a screen that some crystals cannot pass through. That is the requirement for cells to contain biomolecules and to be wrapped in a membrane. A “biomolecule” is simply an organic (containing carbon) molecule produced by a living creature (22). Obviously this criterion is impossible for a crystal not containing carbon, i.e. inorganic, to meet. But many crystals are organic (23). And therefore all of those, except those solely of carbon, contain biomolecules, if it is granted that crystals are alive. Yet if one grants that crystals are alive, obviously the current scientific conclusion that all life as we know it is carbon-based (25), dissolves. Furthermore, the article referenced (25) goes on to accept the possibility that, although the carbon atom seems the most suited for life, life forms could be based around other elements such silicon or germanium. Why, then, should the definition of life be shackled to carbon?

The next hurdle, however, seems too lofty to leap: the unit cells of these crystals are not surrounded by any membranes. This shortcoming is perhaps excusable because nothing is surrounded by a physical, as opposed to an electrical, membrane at the molecular and atomic levels. Organic cells are enormous in comparison to unit cells. For example, a red blood cell is eight micrometers across (39) and a unit cell of Nickel is about 350 picometers across (40): the red blood cell is about a little under 5000 times larger than a unit cell of nickel, length wise, and even more astronomically tiny by volume. Since membranes, in general, are made up of molecules, how could something the size of a molecule, such as a unit cell, have a membrane? Additionally, if one could grant, for the purposes of argument, that crystals are alive, they would be an entirely different sort of living creature from those biologists are accustomed to. There is no reason to assume that such an entirely different form of life would necessarily depend upon membranes.

In sum, it has been determined that crystals are composed of cells, granted a general definition of the term.

Do crystals have metabolism?

            Crystals are now going to tested by the second criterion: the capacity for metabolism. As above, the discussion will begin with a definition; the Cambridge Dictionary (24) defines metabolism as “the chemical and physical processes by which a living thing uses food for energy and growth.” The previous section on the cellular composition of crystals explained that crystals do grow. Their “food” is comprised of the elements that constitute them. These elements align themselves into the crystal lattice, so the crystal is using their energy to grow. This growth will be covered in further detail in the following section. Crystals, then have a capacity for metabolism.

Can crystals grow and develop?

            Closely related to metabolism is the capacity for growth and development, the third criterion. Anabolism is the specific term for growth (26).  Crystals can grow out of supersaturated solution (20), vapor, and solid mineral deposits (27). The process by which crystals grow has been explained above. As crystals grow, they attain a greater size and their individual compliment of defects and impurities. This is the unequivocal growth and development of a crystal.

Can crystals reproduce?

            The next criterion and perhaps the most important is the capacity to reproduce. Reproduction simply means “the production of offspring by organized bodies” (28). In addition to being able to form naturally by nucleation (19), crystals can form much more quickly by a process called seeding. Seeding involves placing microscopic crystals into a favorable environment for crystallization to accelerate the growth of crystals (29). This is the way in which a crystal reproduces: a piece of a crystal is chipped off the parent and the chip, or seed, carries the information to form new crystals in its unit cells. When it finds a favorable environment abundant with “food”, new crystals, or offspring, are made. This process is asexual, because the offspring are clones of the parent (28).

            The offspring described in the previous paragraph cannot rightly be offspring if they don’t share characteristics of their parent through heredity, the capacity for which is the fifth criterion. The offspring of asexual reproducers are clones of the parent and have essentially identical features. This is, of course, untrue if the offspring grow up in a much different environment than the parent did, and develop differently. The way in which crystals pass their traits to offspring is through a universal code that defines the structure of each crystal. The crystal structure acts as the blue print, like DNA for a new organic organism, a new crystal.

Unfortunately, this process cannot meet the definition of heredity which is complex and restrictive. Heredity is defined as the natural process by which parents pass genes to offspring (30). Genes are chemical patterns on chromosomes that shape the development of offspring (31). Crystals cannot be said to have this characteristic. However, the purpose of genes is to shape the offspring to be like the parent. Although the process described above cannot be called heredity in the strict sense, it clearly accomplishes the same thing. If crystals are a new life form, they have simply found a different way of passing on their characteristics to offspring.

Do crystals maintain homeostasis?

            Every living organism needs a specific needs a specific set of conditions to survive; temperature, pH, salinity, etc must all be within a certain range for a given creature to live. Internal conditions are even more important than external ones. Homeostasis is the process that an organism uses to maintain the same internal conditions despite external changes (32). These processes only work within limits, of course: if a human were plunged into the Sun, homeostasis would not help it.

Crystals have something which could be thought of as homeostasis: an equilibrium crystal shape (ECS). ECS is the shape of a crystal at which it has minimum surface free energy, given a constant volume (33). This is the shape at which a crystal is “happiest.” To demonstrate,  imagine a crystal at its ECS. If one filed off a corner, after a while the crystal would reorganize itself back into the ECS (34). A NASA article acknowledges that crystals can maintain equilibrium (2). These data affirm that crystals perform homeostasis.

Can crystals respond to stimuli?

            Probably the easiest criterion to satisfy, the capacity of life to respond to stimulation, is considered next. Several pieces of information already provided exemplify response to stimulation. The homeostasis of crystals described above constitutes a response to stimulation. Also, liquid crystals can respond to light, heat, and mechanical stress (35). Certain photonic crystals are responsive, as well (36). The aforementioned NASA article (2) also states that crystals can “move” in response to stimuli. Surely this point is affirmed.

Can crystals evolve?

            The final criterion: The capacity to evolve through adaptation. This is, arguably, the characteristic furthest from relevance to the discussion, because it is unclear and hitherto unproven whether bodies normally considered alive today do indeed evolve (3). However, according to the article referenced, there is an enormous collection of data that perhaps the majority of scientists think validates the evolutionary process, as described by a website entitled “Understanding Evolution” (14). Seemingly, though, another individual could consider the facts and develop a different interpretation, or theory. Furthermore, Steven Benner in an article entitled, “Defining Life” (8) describes how fictional characters, such as androids, that humans today would be forced to consider alive, would not be subject to Darwinian evolution.

Benner posited that humans would acknowledge the living status of such hypothetical creatures, based on our “values” concerning what is alive. For example, if an unconventional being such as a cloud were to float one day into a person’s path, and verbally refused to move, displaying sentience, could that person consider the cloud dead? The capacity for evolution does not seem to be one of the characteristics of life familiar to us that people value, such as response to stimulation, reproduction, etc. The reason for this may simply be that evolution is  not observable. It is inconsequential to transient individuals. In fact, most creatures, including some humans, normally only think about reproduction, growth and development, and response to stimuli. The other, less visible ones, such as heredity and cellular composition, are at least observable within a lifetime.

If this weren’t enough, some definitions for life completely exclude the capacity for evolution as a criterion (37). So even if crystals do fail this test, that will not negatively impact their prospects of meeting the criteria of accepted definitions. But, for the purposes of argument, let us assume universal evolution to be true; Do crystals undergo this process?

To answer this question the Cairns-Smith theory will be considered. It stipulates that the first organic life arose from clay crystals that stored and replicated a genome simple enough to have spontaneously arisen (38). The article referenced explores how hypothetical clay crystals might have evolved due to resource scarcity. An ability of crystals to run programs that predict the most abundant resource available in their environment, which would allow crystals to grow faster, might have developed. The research in the paper concludes that it is conceivable for real crystals to have evolved into responsive, sensitive, creatures. This is no real evidence, but a possible proof of concept.

Although this paper has failed to demonstrate that crystals evolve, and therefore failed to completely satisfy the definition it set out to, other definitions that, perhaps rightly, exclude the evolution criterion, have been satisfied.

Cybernetic definition of life

            The textbook definition scrutinized above is not the only proposed definition of life. A cybernetic definition defines life as a network of regulatory mechanisms subordinated to a potential for expansion (9). Crystals certainly possess a network of regulatory mechanisms, and harness these to expand. Unless that extrapolation harbors a misinterpretation of the cybernetic definition, crystals do satisfy it and contain “the essence of life” which, as the authors of the referenced article suggest, the cybernetic definition embodies.

Value based definitions of life

            A previously referenced article mentioned that one way of determining whether or not something is alive based on our values (14). People in general seem to value life for its responsiveness, its growth and development, and its reproduction. The one of those features that isn’t obvious in crystals is responsiveness, although they do possess this characteristic, as argued above. More importantly, though, they don’t respond in ways that humans can naturally interpret. This lack of intuitive understanding is probably a reason why people generally do not consider crystals alive.

At first glance, a coral reef may look inanimate, but with a scientific background one knows that they are alive. Science has provided this viewpoint. It is hard for the unaided human to observe the living properties, such as growth, of a coral reef. Crystals naturally grow very slowly as well. This slow growth of crystals is perhaps another reason that crystals aren’t considered living.

In contrast, a tree seems to grow just quickly enough for people to observe considerable growth in a lifetime. In addition, trees are far more abundant and ubiquitous. Crystals, however, are less obvious and generally paid less attention. Seemingly, for a long time humans in general failed to observe these important characteristics of crystals as a consequence of there inattentiveness and short life spans. Yet, when science began to study crystals, it was too late: people had already developed a system of somewhat arbitrary values that determined in their minds what was alive and what was not. 

In consequence, humans have thought nothing of harvesting and exploiting crystals for their beauty and their great utility in electronics, building, etc. However, this would not be surprising even if humans did consider crystals to be alive. Consider what they have done to creatures in the modern farming and livestock industries. Obviously nothing can be done for the unfortunate case of crystals while those atrocities on more obviously living things (including humans) continue. Of course all living creatures depend on each other for survival, but humans have learned to satisfy their greed for wealth and convenience at an unprecedented level, to the detriment of all life, crystals (perhaps) included.


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The Lead and Iron Oxides

Here is a chemistry paper on the lead and iron oxides that I wrote in September of 2018. It provides definitions for the terms “compound” and “oxidation”, as well as giving physical and chemical descriptions of each of the three oxides of lead and the three oxides of iron. I hope you learn something, enjoy, and, if you have a question, ask in the forums!

Lead and Iron are two elements most ancient in their utilization by humans for a vast array of tools and products from swords to ceramics. Quite often, however, they were used in impure forms as oxides. Here a brief explanation of oxidation might prove useful: oxidation is an example of a chemical reaction, which is any interaction between atoms of one or more elements in specific ratios to form a new substance, called a compound (“Definition of Compound”, 2017, pp. 1). The constituents of the compound become chemically bonded and cannot be separated by physical means (“Definition of Compound”, 2017, pp. 1). The resulting compound may have entirely different properties from the constituents (Chemical Reactions, n.d.). One way to form such compounds is by oxidation, the process by which one element, the oxidizer, accepts electrons from another element thus becoming bonded to it (Clark, 2016). Oxidation was named after the gaseous element oxygen, because oxygen is an oxidizing element, as is it highly electronegative, eager to steal electrons. In fact, oxidation was originally understood as in terms of oxygen transfer, rather than the more accurate model of electron transfer (Clark, 2016). Lead and iron are both more electropositive than oxygen, so they will be oxidized in a reaction with oxygen. Depending upon the conditions in which this reaction takes place, it can lead to several different compounds with different properties and uses (Winn, 2004).

Beginning with iron, the first possible compound is a mineral called hematite. Hematite, or Fe2O3, is one of the most common minerals in the world, and is present, at least in small amounts, in many rocks, e.g. sandstone, that have a reddish or brownish coloration, caused by the presence of hematite, although the mineral itself can vary greatly in color, from gray to silver-gray, black to brown and reddish brown (Winn, 2004, pp. 1). In fact, hematite was used until recently to make a dye of the latter color, before cheaper alternatives were developed. It is also responsible for the coloration of Mars, the Red Planet (Winn, 2004, pp. 2). Although it is only paramagnetic under normal conditions, it becomes strongly magnetic when heated, similar to another iron oxide, magnetite. Its hardness ranges from 6-7 on the Mohs Scale, and it may contain small amounts of Titanium. As the principle ore of iron, hematite is mined for the industrial production of iron and is the source of approximately ninety percent of all iron. Fine mineral specimens can be found in several localities, including Minas Garais (Brazil), Cumberland (Cumbria, England), and Ria Marina (island of Elba, Italy). (Friedman, “The Mineral Hematite”, 2018). The chemical reaction that forms hematite looks like this:

4Fe+3O2→2Fe2O3 (Winn, 2004)

That is what happens if there is ample oxygen available, but a different result occurs if the oxygen is less plentiful: Fe3O4, or magnetite. Notice that magnetite has higher iron to oxygen ratio than its cousin, hematite. (Winn, 2004, pp. 4)As referenced before, magnetite earns its name for being a natural magnet and the only mineral with this property. In coloration it is dark gray to black with a hardness slightly greater than hematite at 5.5-6.5. It also differs from its duller cousin in luster, having a metallic luster. Like hematite, though less widely used, it is an important ore of iron. It is of scientific interest due its pronounced magnetic properties. Magnetite can be found almost anywhere around the world, but there are a few noteworthy sources, such as Binn Tal (Wallis, Switzerland), Parachinar (Pakistan), and Cerro Huanaquino (Potosi, Bolivia). (Friedman, “The Mineral Magnetite”, 2018). The chemical reaction that forms magnetite looks like this:

6Fe+4O2→2Fe3O4 (Winn, 2004)

The final oxide of iron is known wüstite. This compound was named after geologist and paleontologist Ewald Wüst (1875-1934) of the University of Kiel in Germany. Wüstite has a hardness of 5-5.5 and occurs mainly in meteorites and anthropogenic slags. (“Wüstite”, 2018). Although its chemical formula is often given as FeO, it breaks the law of definite proportions; the ratio of iron to oxygen ranges between 0.85-0.95/1. Because of this, it is known as a nonstoichiometric compound. This technically allows for an almost infinite number of iron oxides, but all the non-stoichiometric oxides of iron are categorized as wüstite. (Winn, 2004, pp. 9)

Despite this anomaly, most compounds do have distinct stoichiometries, like the lead oxides. first lead oxide is lead monoxide, or PbO. It forms when is heated in the presence of oxygen and can take one of two forms, litharge or massicot, differentiated by their crystal structure. Both are yellowish solids, litharge has a tetragonal crystal structure and massicot has an orthorhombic crystal structure. (“Lead”, 2018, pp. 12). They both have a hardness of 2 on the Mohs scale and have dull, greasy lusters. Litharge has a variety of uses, including in lead acid batteries, glazing pottery, pigments, lead glass, and oil refining. Litharge mines occur on every continent of the world, with an especially high concentration in European countries, such as Sweden, the United Kingdom, and Germany. (“Litharge”, 2018). Massicot mines can be found in many countries around the world, including Madagascar, Namibia, Australia, and Germany (“Massicot”, 2018).

The second lead oxide is known as minium, after the Minius river located in the Northwest of Spain. The chemical formula is Pb3O4, lead tetroxide. Another name for it is red lead, because it can be made into a beautiful read pigment that has been used in paintings since the time of the ancient Romans. Paintings made with minium are called miniatures. (“Red Lead”, n.d.). The hardness of minium is 2.5, and it has a tetragonal crystal structure just like litharge, with a similar luster. Mines are concentrated in Europe but can be found on every continent. (“Minium”, 2018).

The final oxide of lead is plattnerite, otherwise known as lead dioxide (PbO2). It was named in honor of Karl Friederich Plattner (1800-1858) who served as professor of metallurgy and assaying at the Bergakademie of Freiburg in Saxony, Germany, by Karl Wilhelm von Haidinger. It is a brown to black mineral that is commercially produced in a process involving the oxidation of the lead oxide previously discussed, minium, by chlorine (“Lead”, 2018, pp. 13). Plattnerite is used in curing polysulfide rubbers, matches and pyrotechnics, and dyes (“Lead”, 2018, pp. 13). The hardness of plattnerite is 5.5 and it has a dull, metallic luster. The plurality of plattnerite mines are in North America, and of those approximately half are in Mexico and half are in the United States, concentrated in the Western side of the country. (“Plattnerite”, 2018).

These three oxides of iron and three oxides of lead are all very useful and very different from each other. This demonstrates the power of chemical reactions, to take the same two elements in different proportions and create new substances with different properties. However, as was touched on briefly, the chemical composition of a compound is not the sole determining factor of the properties of a substance; other factors, such as crystal structure, also play very important roles, as seen in the two forms of lead monoxide, litharge and massicot (“Lead”, 2018, pp. 12). Regardless of their composition and crystal structure, human beings have used the six oxides discussed above for a long time, some for millennia (“Red Lead”, n.d.), and will probably continue utilizing these useful compounds long into the future.


“Chemical Reactions”. (n.d.). Retrieved September 4, 2018, from 

Clark, J. (2016, May 1). Definitions of Oxidation and Reduction. Retrieved September 3, 2018, from 

“Definition of Compound”. (2017). Retrieved September 3, 2018, from 

Friedman, H. (2018). The Mineral Hematite. Retrieved September 3, 2018, from 

Friedman, H. (2018). The Mineral Magnetite. Retrieved September 3, 2018, from 

‘Lead”. (2018). Retrieved September 3, 2018, from 

“Litharge (Lead(II) Oxide), Lead Monoxide”. (2018). Retrieved September 3, 2018, from 

“Litharge”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from 

“Massicot”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from 

“Minium”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from 

“Plattnerite”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from 

“Red Lead”. (n.d.). Retrieved September 2018, 2018, from

Winn, J. S. (2004, January 6). Stoichiometry of Iron Oxides. Retrieved September 3, 2018, from 

“Wüstite”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from 

A Short Exposition of Photosynthesis

Here is a short research paper on photosynthesis, that most wonderful and complex phenomenon that makes life possible. It deserves much deeper treatment that a short, high-school level report, but I hope this will provide a decent starting point on your learning journey. Don’t forget to ask your questions in the forum!

Photosynthesis is the process by which energy from the sun is used to chemically combine carbon dioxide (CO2) with water (H2O) to make oxygen and glucose. Green plants, i.e. plants with chlorophyll, and some other organisms utilize this chemical reaction to make food. Plants are primary producers occupying the lowest trophic level. They support all higher trophic levels and thus their level has the highest biomass. Without photosynthesis, most life on Earth would not exist. (1).

            The majority of photosynthesis in plants takes place in the middle layer of the leaves, or the mesophyll. The cells in the mesophyll are equipped with organelles called chloroplasts, specifically designed for carrying out photosynthesis. Inside the chloroplasts are what resemble stacks of coins. Each coin is called a thylakoid and has a green pigment called chlorophyll in its membrane. The entire stack is a called a granum. The grana are occupy a fluid-filled space called the stroma. (1).

            Photosynthesis is actually a complex series of chemical reactions, some being light-dependent and others being light-independent. The light-dependent reactions take place in the thylakoid membranes where the chlorophyll absorbs light which is converted to adenosine triphosphate (ATP), an energy carrying molecule, and NADPH, an electron carrying molecule. It is here that the oxygen we breathe is created from water as a byproduct and diffuses out through the stomata, tiny pores in the surface layer of leaves letting oxygen diffuse out and carbon dioxide diffuse in. (1).

            Then begin the light-independent reactions that are collectively known as the Calvin cycle. They occur in the stroma and use the ATP and NADPH to fix carbon for use in constructing cells and form three-carbon sugars, glyceraldehyde-3-phosphate, or G3P, molecules,  that link up to make glucose. (1).

            In summary, the heat energy from sunlight ends up stored as chemical energy in the bonds of the sugar molecules that can be metabolized by plants and other organisms. (1). The reaction absorbs heat so it can be described as endothermic. (2).


  1. “Intro to Photosynthesis.” (2018). Khan Academy. Date-accessed: 5/14/2018.

2. Helmenstine, Anne Marie. (2018). “Endothermic Reaction Examples.” ThoughtCo.

Why the Statue of Liberty is Green

The Statue of Liberty with its iconic green color.
The Statue of Liberty, image retrieved from the National Park Service (4).

The Statue of Liberty is an iconic national monument on Liberty Island that was dedicated on October 28, 1886 (1). Back then, it was not as we see it today; then the exterior was copper colored, because, of course, it was made of copper! But today it is tiffany blue (2) to mint to seafoam green (3), depending upon the lighting (1, see image) (4). This was the result of a series of chemical reactions that took place over the first thirty years after the statue was assembled (5) and provide the reason why the Statue of Liberty is green.

            The first reactions involve a concept called reduction in chemistry. Reduction occurs when an atom that is being oxidized donates electrons to the oxygen atoms. Chemists say that the oxygen atoms have been reduced. (6). They assign an oxidation number to the atom being oxidized that indicates the number of electrons gained or lost by that atom: a positive oxidation number means electrons have been donated and a negative oxidation number means electrons have been gained. Since oxygen is highly electronegative, it is eager to steal electrons. So oxygen tends to take electrons, which reduces its charge. That is the origin of the term “reduction.” Oxygen is more electronegative than most other elements, so in a reaction it is generally the atom that takes electrons and the it is generally the other atoms that give electrons, since they are more electropositive. (7). Since most elements tend to donate electrons to oxygen, the losing of electrons to another element is called “oxidation.” Reduction and oxidation are opposites, but they always go together. Thus, a reaction involving the giving and taking of electrons is called a redox reaction. (6).

            In the first reaction, the copper is oxidized, by oxygen (which is reduced), to form CU2O. This compound is pink or red. Then the copper cation continues to react with oxygen to form copper oxide, 4CuO, which is black to brown. In the first years after Libertas’ figure was erected near New York City, much coal was burned in that city. The resulting air pollution wafted over the Statue of Liberty, bringing with it sulfur. This reacted with the copper to form the compound 4CuS, which is black. Three final compounds form from these initial compounds with the addition of carbon dioxide and hydroxyl ions: CuCO3(OH)(green), Cu3(CO3)2(OH)2 (blue), and Cu4SO4(OH)6(green). (8).

            These three compounds form the iconic blue-green verdigris that encases the Statue of Liberty today. The Statue of Liberty provides a great lesson in chemistry about redox reactions and successive reactions.


  1. “Liberty Enlightening the World.” (n.d.).National Park Service. Date-accessed: 4/10/2018
  2. Knapton, Sarah. (2017). “First new shade of blue discovered for 200 years to be turned into Crayola crayon.” See image at end of article. The Telegraph. Date-accessed: 4/10/2018.
  3. Morris, Brian. (2015). “50 Shades of Green…and One Shade of Blue.” PsPrint. Date-accessed: 4/10/2018.
  4. “Plan Your Visit.” (n.d.). National Park Service. Date-accessed: 4/10/2018
  5. “Why is the Statue of Liberty Green?” (2018). Wonderopolis. Date-accessed: 4/10/2018.
  6. Clarck, Jim. (2016). “Definitions of Oxidation and Reduction.” LibreTexts. Date-accessed: 4/10/2018.
  7. “Oxidation-Reduction (Redox) Reactions.” (2018). Khan Acandemy. Date-accessed: 4/10/2018.
  8. Helmenstine, Anne Marie. (2018). “Why is the Statue of Liberty Green?” Thought co. Date-accessed: 4/10/2018.

The Chemical History of Aluminum

An example of aluminum in use
Aluminum electric line, used for light weight and decent conductivity.

Aluminum is an essential component in a myriad of modern conveniences from airplanes to pop cans, prized for its high strength to weight ratio and resistance to atmospheric corrosion. This silvery-white metal was even more highly valued in the time of Napoleon III, more even than gold. However, this was merely for its extreme rarity rather than for its applications in manufacturing. This only changed when two young chemists, American Charles Martin Hall and Frenchman Paul Héroult, standing on the shoulders of other notable scientists before them, discovered a chemical method to economically extract pure aluminum from its ores. Their method was only the latest in a long line of attempts in the history of aluminum, but it was the first to be commercially utilized on a large scale and is still in use today. (“Commercialization of Aluminum”).

However, for thousands of years aluminum was not even known to exist, despite its use in compounds predating 5000 BC. Ancient Mesopotamians used aluminum-rich clays to craft fine pottery. In addition, aluminum compounds were utilized by Ancient Egyptians and Babylonians as medicines almost 4,000 years ago. And from the ancient world to the medieval period, an aluminum compound, known as alum today, was used to bind dyes to textiles. However, it was not until the eighteenth century that anyone suspected that a metal could be found in these useful compounds. (“Hall-Heroult”).

Aluminum is Christened

Humphry Davy, an English chemist, made the first attempt to extract this metal in 1807. It was made after a long string of successes in isolating pure metals from compounds, such as potassium from potash and sodium from salt, using a method called electrolysis. (Pizzi). Electrolysis is the process of running a direct electrical current from a battery or other source through an ionic solution called an electrolyte using two metal bars as electrodes. The electrons flow from one electrode to the other making one, the cathode, negative and the other, the anode, positive. Positive ions, cations, in the solution are attracted to the cathode and negative ions, anions, are attracted to the anode. When the ions reach their respective electrodes, electron exchange occurs causing a chemical reaction. In this way pure elements can be separated from compounds. For example, if two copper electrodes connected to a power source were inserted into a solution of molten salt, sodium chloride, the negative chloride ions would be attracted to the anode and the positive sodium ions would be attracted to the cathode. At the cathode, the sodium ions would transfer their excess electrons to the cathode and would become neutral. And the same thing would happen to the chlorine ions at the anode, except here there would be a gain of electrons for the chloride ions. The reactions would look like this: (“Electrolysis”).

​At the cathode: Na++ e- → Na

At the Anode: 2Cl- → Cl2 + 2 e-

​Although Davy failed to extract aluminum from alum in this way, he satisfied himself that the metal existed and named it alumium, afterwards rechristening it as aluminum. (Pizzi).

Aluminum is Isolated

​The first sample of aluminum was obtained in 1825 by Danish scientist Hans Christian Oersted who heated a mixture of aluminum chloride and potassium-mercury amalgam under reduced pressure. This caused the mercury to boil away leaving an impure sample of aluminum. (Ashby). This chemical reaction was as follows (Caroll, 5):


Using a similar process but with metallic potassium instead of potassium-mercury amalgam, German chemist Friederich Wohler distilled aluminum pieces up to the size of pinheads by 1840. From these samples, he determined the properties of aluminum such as ductility, color, and specific gravity. This made aluminum available, but only at the hefty premium of approximately 545 dollars per pound (1852 dollars). (“The Element Aluminum”).

The Deville Process

Thus, aluminum remained a mere curiosity until 1854, by which time French chemist Henri Saint-Claire Deville had successfully implemented his improvements on the methods of Wohler, namely the substitution of sodium for the more expensive potassium, to produce globules of aluminum the size of marbles using the following method: (“Deville-Castner Process”).

​Deville’s goal in aluminum manufacture was to reduce sodium and aluminum’s double chloride, 2NaClAl2Cl, using heated metallic sodium. The natural first step, then, was to manufacture the double chloride. This process was begun by taking powdered aluminum oxide, or hydrate of alumina (Al2O3+water), and combining it with lamp-black, salt, and charcoal. The resulting mixture was then moistened and processed in a pug mill before being extruded through dies, cut into three-inch cylinders, and dried. These cylinders were then precisely heated in an atmosphere of chlorine gas which causes the desired double chloride to evaporate from which gaseous form it was condensed into a pale-yellow, deliquescent material pungent in odor. The reaction that produced this most important ingredient was as follows: (“Deville-Castner Process”).


Translated into English, the reaction is alumina plus carbon plus salt plus chlorine gas equals double chloride plus carbon dioxide.

Now all that had to be done was the reduction of the double chloride using sodium. To this end, the double chloride was pulverized and mixed with slices of metallic sodium before being heated in a furnace along with cryolite, Na3AlF6, as flux. This resulted in the following reaction: (“Deville-Castner Process”).

2 (Na Cl) Al2Cl6 + 3 Na2 = 8 Na Cl + Al2.

​This simply means that the double chloride chemically reacted with the sodium to produce the desired aluminum and a byproduct of salt. This alone reduced the price to 115 dollars per pound, but the price did not solely depend on the quantities of aluminum that could be obtained.

​The cost of the materials used in aluminum manufacture, a very important one of which was sodium, was a very important factor influencing the price of aluminum. Until 1886 when a man named Hamilton Y. Castner began developing a safe, inexpensive method, sodium production had been very arduous and perilous. Involving electrolysis, the Castner process (completed in 1888) reduced the price of sodium five-fold. Although this development made aluminum more affordable, it was still prohibitive enough to keep aluminum from widespread use. (“Deville-Castner Process”).

The Hall-Heroult Process

​While these achievements represented giant leaps forward in aluminum production, the greatest and yet unsurpassed method was still to come. This discovery was twice made independently by two twenty-two-year-old chemists during the same year that Hamilton Y. Castner developed his sodium production process, 1886. Charles Martin Hall, an American graduate of Oberlin College in Oberlin, Ohio,, worked with Oberlin College professor Frank Fanning Jewett to develop the following process: (“Hall-Heroult”).

First, alumina is dissolved in a vat of molten cryolite at a temperature of 982 degrees Celsius (Ashby), acting as a flux as in the Deville process. Then, it, the electrolyte, is channeled into a cell with a carbon-lined cast-iron shell. Carbon anodes are suspended in the electrolyte and the carbon lining acts as a cathode. An electric current is passed through the cell and the dissolved alumina separates into its constituents, oxygen and aluminum. The molten aluminum sinks to the bottom of the cell and the oxygen remains around the anodes. This involves two half-reactions, reduction of the aluminum at the cathode and oxidation of the oxygen at the anode: (“Extraction of Aluminum”).

Reduction: Al3+  +  3e-       Al

Oxidation: 2O2-  –  4e-       O2

These two half reactions can be combined into one whole reaction which is as follows (“Extraction of Aluminum”):

2Al23+O32-(l)                 4Al(l)   +     3O2(g)

​Paul Louise Toussaint Heroult independently discovered this same process just two months after Charles Martin Hall. He applied for and received a patent for it in France and applied for one in the United States in May of 1886. Although this was before Hall applied for his patent in July, Hall was able to prove that he discovered the method before Heroult made his patent application. Two years later, Hall founded the Pittsburg Reduction Company with financial assistance from six industrialists involved in Pittsburgh’s metallurgical market, including MIT graduate Alfred Hunt. That same year, the price of aluminum plummeted to $4.86. By 1993, the price had dropped to seventy-eight cents per pound. And by the 1930s, it aluminum was valued at just over twenty cents per pound. (“Hall-Heroult”). This remarkable figure was not, however, achieved by Hall and Heroult alone.

Two other notable developments aided in the commercialization of aluminum, namely the dynamo and the Bayer Process. Without the former, none of what Hall and Heroult achieved would have been possible. Invented by Siemens, Hopkinson, and Edison in 1881, it provided the power source necessary for electrolysis. Later, aluminum companies moved to places where abundant hydroelectric power could be found to drive the dynamos. While the dynamo and hydroelectricity made inexpensive electricity abundant, the Bayer process cheapened the raw material for aluminum production, alumina. As the Castner process cheapened sodium, the Bayer process cheapened the production of alumina. (Ashby).


​Use of aluminum began several millennia ago in pottery and medicine, but it was not until relatively recently that it was discovered. Over the years, better and better methods were devised for aluminum production and the production of ingredients involved in its production. This continued until the price, once greater than that of gold, was reduced sufficiently so that the full industrial potential of aluminum could be realized. This was achieved in large part by the work of Charles Martin Hall and Paul Louise Toussaint Heroult in 1886. (“Hall-Heroult”). These young chemists were heirs to the work of several other notable chemists who made important contributions to the field of aluminum including Humphrey Davy, Hans Christian Oersted, Friedrich Wohler, Henri Saint-Claire Deville, Frank Fanning Jewett, Hamilton Y. Castner, and Karl Joseph Bayer. Standing on the shoulders of these intellectual giants and using new technologies of their day, Hall and Heroult were able to make aluminum available for widespread use.

Works Cited

​”Aluminium and Its Manufacture by the Deville-Castner Process.” (1889). Science, 260-262.

​Ashby, J. (1999). “The Aluminium Legacy: the History of the Metal and its Role in Architecture.” Construction History, 79-90. Retrieved from:                                                                              

“Commercialization of Aluminum.” (2001, November 2). Retrieved November 11, 2018, from                                                                      

Dr. William F. Caroll, Jr. (2012, April). “From Garbage to Stuff: How we Recycle Plastics.” The Alembic, 39(3), p. 5. Retrieved from                       

Education, T. J.-O. (n.d.). “The Element Aluminum.” (G. Steve, Editor) Retrieved from Jefferson Labs:                                                                         

“16.7: Electrolysis: Using Electricity to Do Chemistry.” (2018, May 4). Retrieved November 11, 2018, from LibreTexts.

“Extraction of Aluminium – Hall (Electrolytic) Cell.” (n.d.). Retrieved November 11, 2018, from                                                        

Pizzi, R. A. (2004). “Humphry Davy, Self Made Chemist.” Chemistry Chronicles, 49-51.

“Production of Aluminum: The Hall-Héroult Process.” (2018). Retrieved November 11, 2018, from American Chemical Society: