The World of Mineralogy

Mineralogy and Mineral Collecting

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Interview Special

In order to learn more about minerals and mineral collecting we decided to interview a local geology professor well known for his extensive mineral collection and passion for the field.

Q: What species of minerals are most popular with collectors these days? Why?

 A: “Well that’s a bit of a difficult question to answer. I’d have to say that it really depends on the individual collector. Some people like collecting very specific things. For instance there are people who just collect various morphs of Calcite and that’s it. However, I think I can say that quartzes are perennially popular amongst collectors due to their wide range of colors and morphology.”

 Q: How are “high-grade” minerals sorted from industrial material at the mines? Who is in charge of this process?

 A: “Honestly I don’t know for certain how that happens. By the time the samples get to me they has already happened. I imagine the mine director simply instructs the workers to collect any particularly impressive specimens in an undamaged state. After that the mine would sell them (the specimens) to dealers at a price significantly above their industrial value, hence why they would even bother in the first place.”

 Q: How are high-grade samples shipped from the mines to the dealers? Are brokers usually involved? A: “With lots of bubble-wrap (laughs). I really can’t say for certain, but I would imagine it depends on whether or not the mineral dealer has had contact with the mine previously. The profit margins on collector samples are so high compared to industrial material that it would make sense for there to be brokers and various middlemen, but again, I can’t say for certain.”

 Q: What species of minerals are especially difficult to obtain at this time? Why?

 A: “Well, particularly rare species are perennially difficult to obtain. But samples that come from areas that are currently in a state of war or economic sanction are obviously very difficult to acquire.  Afghan sapphires are effectively impossible to obtain at the moment, for instance. Also species that collectors simply aren’t interested in are obviously difficult to obtain. Generally speaking, the more people want a particular species the more easily it can be had. Supply and demand.”

 Q: Are there regional variations for the types of minerals that are in demand? What are the reasons for this?

 A: “ I assume by that you mean do people from different countries have different taste in minerals? (The interviewer responded in the affirmative). Well then, in that case of course. I’m not a culture expert so I couldn’t tell you why, but it’s well known that certain cultures value specific rocks and minerals more than others. The Chinese have always held nephrite and jadeite in very high esteem, for example. Or there’s the Western obsession with diamonds. I’m sure there are other examples as well, but those are the two that come to mind.

 Q: What advice do you have for the mineral collector looking to expand his or her collection? Do you recommend any specific species? Why?

  A: “Hmmm. I would say that the most important thing is to get something you actually like. Even if you already have ten different samples of calcite if you see a specimen of dogtooth calcite that you absolutely adore, go for it. I don’t think you should necessarily get a sample just to check off a box on the species list, unless that is your end goal. As for specific species to get I can’t really say. One thing I will mention is that I feel many mineral collectors, especially those new to the hobby, often neglect the more ‘industrial’ mineral species in favor of those that look more like the popular image of ‘crystals.’ I believe this is a mistake. Sure, a piece of stibnite isn’t translucent and glassy like a piece of quartz, but it is beautiful in its own way and certainly a lot more unique.”

An amazing interview with a veteran in both the academic world and in the hobby. Truly a treasure trove of valuable knowledge regarding mineral collecting.

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Today Subsolidus will be giving a special presentation on loupes (hand lenses). This is intended to be an introductory video for viewers unfamiliar with what a loupe is.

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The Purity of Brimstone

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What is a mineral? The question seems simple. It is a pure inorganic compound that is naturally occurring and can be found in the Earth. But what about substances that only partially fit this definition? Anthracite is a naturally occurring pure compound that can be found in the Earth, but it is biogenic in origin, all of the carbon contain in a piece of anthracite is derived from living organism. Is anthracite a mineral? What about crude petroleum? Or what about mercury? Mercury is a naturally occurring pure substance d that is found in the Earth. But it is a liquid with no crystalline structure, and it is a pure element not a compound. Are any of these materials minerals? Clearly our definition of what is a mineral is far from perfect. The natural world has an incredible diversity that so often defies categorization.

 So far all of the minerals we have examined have been “minerals proper.” They fit the textbook definition perfectly. They have a determinate chemical composition, are naturally occurring, are found in the Earth, and are inorganic. Naturally, today we will be looking a substance that doesn’t quite fit that mold. The substance we are looking at today is Sulfur.

 Sulfur is a substance that humans are almost universally familiar with. The word “sulfur” brings to mind thoughts of pungent odors, gunpowder, and the color yellow. Indeed, sulfur has all of these attributes. But why are we discussing it in a mineral blog? It is because sulfur, despite not being a chemical compound, is actually classified as a mineral.

 Despite minerals commonly being thought of as chemical compounds there are a number of minerals that are not at all compounds, but are in fact pure elements. This means that they are comprised of a pure single element without anything else in them. Copper, Silver, Gold, Mercury, Tin, and, of course, Sulfur, can all be found in a more or less naturally pure state in the Earth. In these instances they are considered to be minerals. However, in the case of the metals the term “native metal” is more commonly used, and is generally preferred.

 Sulfur is an enormously useful material. In addition to being an essential nutrient for all metazoans including humans it is one of the most significant industrial materials in the world. Every year thousands of metric tons of sulfur are consumed by the chemical, fertilizer, and pharmaceutical industries. Without cheap and highly pure sulfur the modern world would grind to a halt.

 From a collector’s standpoint, native metals and elemental minerals provide many unique and beautiful possibilities. Even sulfur, a proletariat material if there ever was, can be a beautiful and unique sample. Big samples can have large crystalline faces that reflect light with a characteristic waxy luster. Sulfur has a certain translucency to it that is unlike most other materials; it seems to reflect light internally as well as externally. A good piece of sulfur is practically a necessity in any mineral collection. Just don’t mind the smell.

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Guest Post: Lapis Lazuli

This is a guest post by http://expressivebelieveablecharacters.tumblr.com a wonderful blog that is about character expressions in art and animation

Guest Blog Post

In this post I will actually be switching topics to Mineralogy as a guest blog post for http://subsolidus.tumblr.com/ and write about the gemstone Lapis Lazuli.

Lapis Lazuli is a gemstone of a opaque blue color popular for its color. In its natural rock form, it is composed of mainly Lazurite, and also white colored Calcite and brass colored Pyrite. The name Lapis Lazuli comes from “lapis” being Latin for “stone”, and “azula” being Arabic meaning “blue”.

Location(s):

It is most commonly found and mined in Afghanistan, which has been a major source of finding Lapis Lazuli for a long time. It can also be found in Russia and Chile. Small amounts of the rock can even be found in the US.

Uses:

Lapis Lazuli is commonly used for jewelry such as bracelets, beads, and necklaces. It can also be carved for sculptures in art. Because the ultramarine color of Lapis Lazuli used to be considered uncommon and rare, the gemstone was considered highly valuable, rare, and expensive.

Lazurite is the mineral that makes up most of the gem stone Lapis Lazuli. Lazurite shares the same chemical formula as Hauyne, but is set apart with its dominance in containing Sulfide.

Chemical formula of Lazurite:

(Minerals.Net, 2015)

References:

http://www.gemstone.org/index.php?option=com_content&view=article&id=117:sapphire&catid=1:gem-by-gem&Itemid=14

http://www.minerals.net/gemstone/lapis_lazuli_gemstone.aspx

http://www.minerals.net/mineral/lazurite.aspx

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Peacock Ore

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So far all of the minerals we have discussed have had a purely gemological interest. None have had any particular value outside of the gem trade. While gems are often one of the first things that come to mind when most people think of “rocks and minerals” they actually comprise only a very small fraction of all economic transactions involving rocks and minerals. The vast majority of all economic activity involving geology revolves around fossil fuels, construction aggregates, limestone for cement, and metallic ores.

 Of all of these economically significant rocks and minerals the metallic ores are, in my opinion, the most interesting. Fossil fuels and aggregate materials are often dull, monochromic, and malodorous, but metallic ores are often shiny, unusually dense, colorful, or even fluorescent. These attributes combined with the rarity of certain species makes them of interest to both the collector and the professional geologists employed by mining corporations.

 The particular species we are examining today is bornite also referred to as “peacock ore” for its spectacular iridescence. Bornite is one of the most important ores of copper globally comprising the majority of copper ore tonnage that is extracted per annum. It is of particular significance in the American Southwest where it is the best and most common ore of copper available, and the only one that is mined commercially as of today.

 The chemical formula of bornite is Cu5FeS4 being a sulfide mineral containing both copper and iron. We can see that the molar ratio of copper to iron is 5:1 which in turn gives a very favorable mass ratio of copper as well. This is not the only benefit however. Due to its chemical composition it is cheaper and easier to extract high purity copper from this ore. It merely has to be oxidized to copper sulfate and then it is extracted in high purity from solution using standard electrowinning equipment.

 Bornite holds a special place it my heart. It is a mineral that is both extremely useful and extremely beautiful. While hardly unique in that regard it does stand apart in being one of the few aesthetically pleasing industrial minerals that is widely available to collectors, and for that reason alone there should be a place for bornite in every mineral collection.

Bornite sample from Arizona, USA. Sample has been treated with hydrochloric acid to improve contrast. All photographs are released under the Creative Commons BY-NC-SA License. 

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Two Sides of a Chromium Coin

For centuries humans have been fascinated with gemstones. These colorful glasslike stones that come from the Earth are often exceedingly rare. This combined with their durability and natural beauty has made them an enduring symbol of wealth and power. Indeed, to this very day every country that has an extant monarchy almost always has a collection of “crown jewels.” But what are gemstones exactly, and what is it that gives them their color for which they are so beloved?

 As it stands the term “gemstone” does not actually have any real meaning in mineralogy or geology. It is a gemological term and every mineralogist will insist (and rightly so) that mineralogy and gemology are two entirely separate fields. Mineralogy is concerned with the physical properties and fundamental structure of mineral species. Gemology is concerned with the subjective aesthetics of those minerals. To a mineralogist emerald, heliodor, morganite, and aquamarine are all the same material. They are all examples of beryl (beryllium aluminum silicate) with slightly different impurities. To a gemologist however, emerald, heliodor, morganite and aquamarine are all entirely different materials with vastly different values and uses depending on the size and subjective quality of the specific sample. It’s the difference between looking at a painting and trying to analyze the chemistry of the paint it is made with, and trying to assign the painting to a specific school of art. Both are important and useful in their own way.

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The samples displayed in the picture above are two of the most famous gemstones; that is the ruby and the emerald. The classic red and green stone the ruby and the emerald are two “gems’ that everyone can recognize. Clearly they are different types of material, and structurally they are, but they share a common feature that provides great insight into how minerals get their color.

 “Ruby” is a gemological name for the red variety of corundum. Corundum is aluminum oxide Al2O3. Its crystal system is trigonal, that is to say a crystal lattice of corundum looks like a rhombohedrum oriented so that one of its apices is pointed upwards to give it threefold rotational symmetry about the normal axis.

 “Emerald” is a gemological name for the green variety of beryl. Beryl is, as stated above, beryllium aluminum silicate Be3Al2(SiO3)6. It is of the hexagonal crystal system. That is to say a beryl lattice would look like a hexagonal prism standing on one of its hexagonal faces.

 The internal structure of these two minerals / gems seems very different, and they look rather different too. One is red and the other is a deep green. So where is the similarity that ties them together? The similarity lies in what gives them their color. In the case of both emerald AND ruby the color is caused by trace amounts of chromium in the bulk materials. It is believed that in both materials the chromium exists as Cr3+ ions in charge coupled and interstitial substitution, yet in the emerald it causes a dark green color and in the ruby it causes a red color. The science of exactly how specific metallic impurities cause colors in minerals is still under investigation. It’s possible that a difference in relative position of the chromium within the crystal lattice is what causes the dramatic difference in color between the two stones. This would make sense given the variant crystal systems between corundum and beryl. However, it remains an area of investigation. Two stones one red and one green, but they both get their color from the same metal.

Ruby and emerald from Hiddenite North Carolina. All photographs are released under the Creative Commons BY-NC-SA License. 

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Rutilated Citrine

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The crystal is a small yellow stone with a crimson heart. While it is one of the most diminutive mineral samples in my collection it is also one of my favorites. Indeed, it has a combination of features that are uncommon by themselves, but when combined into a single sample is exceedingly rare.

 The bulk of this mineral is “citrine.” Citrine is a gemological term that refers to a yellow or orange colored quartz. Quartz is one of the most common minerals in the Earth’s crust. Quartz is comprised purely of Silicon and Oxygen linked in a network of SiO2 tetrahedra. It is a “tectosilicate,” meaning that its crystalline structure is a “framework” of these tetrahedra. It is, in more ways that one, extremely glass-like. It has a vitreous (glass-like) luster and when it breaks it forms a conchoidal (shell or glass-like) fracture. Quartz comes in a variety of aesthetically pleasing colors including clear (rock crystal), purple (amethyst), pink (rose quartz), white (milky quartz), brown (smoky quartz), and, perhaps most uncommonly, yellow (citrine). These colors are determined by the inclusion of various metallic ions in the crystal lattice that cause dislocations and a change in the absorption spectrum of the bulk material. However, in the case of citrine the dislocations in the lattice are believed to be caused primarily by exposure to ionizing radiation instead of metallic impurities. This unusual method of color development is perhaps why citrine is generally far less common than other varieties of quartz. So if the yellow color is due to exposure to radiation what causes the red color?

 The red core is not quartz at all but an entirely different mineral. It happens, somewhat rarely, that certain minerals can actually grow inside another chemically distinct mineral while the first mineral is forming. In this specific case the citrine crystal has a cluster of fine rutile crystals growing inside of it. Rutile is a mineral form of the material titanium dioxide (TiO2). It forms thin acicular (needle-like) crystals. If you look closely you can see how the red part of the sample appears to be comprised of a cluster of blade-like structures. Since those fine blades are individual rutile crystals this is actually the case.

Quartz crystals with rutile growing inside them aren’t incredibly uncommon. What makes this one particularly special is that the rutile crystals are red. Usually rutile is a brown, yellow, or blue color. Red rutile is rather unusual.

In the end what we have is an uncommon form or rutile growing in an uncommon fashion inside an uncommon form of quartz. All of this adds up to a specimen that, while superficially rather boring, holds a lot of unique character and scientific interest. It’s hardly the largest or most impressive mineral I own, but it is certainly one of my favorites.

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Labradorite

Labradorite, a mineral that easily goes unnoticed by the untrained eye. Yet this seemingly uninteresting and economically worthless mineral holds a secret that provides insight into mineralogy, optics, and nanotechnology. 

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If you happen to find a piece of labradorite in the wild you will initially notice nothing interesting. It will be a moderately dense dark colored “rock” with no unusual features whatsoever. However, if you take the same sample and rotate it around in the sunlight you will see something amazing. The “rock” will appear to flash and change colors depending on the angle between the sample and the incoming light. Bright flashes of blue, orange, and red will streak across the dull background; appearing to originate from deep inside the mineral itself. What is this phenomenon and why does labradorite exhibit it?

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The phenomenon you have witnessed is referred to as “schiller” and it is a color that is literally unlike almost every other color on the planet. In order to truly understand this phenomenon let’s learn more about this mysterious mineral. Labradorite is a plagioclase feldspar. More precisely it is a “mixture” of two different types of plagioclase, specifically anorthite and albite. This is important because it is this “mixing” that allows for the color. At this point you might be thinking that perhaps the anorthite and albite are blue and yellow. However, the truth is far more interesting.

 Anorthite and albite are chemically very similar. This similarity allows them to exist as a completely homogenous solution whilst molten. However as the labradorite cools and solidifies something happens. The previously homogenized albite and anorthite separate out into nano-segregated layers of alternating crystals of anorthite and albite. This phenomenon is referred to as “subsolidus exsolution” and is directly responsible for the colors labradorite shows.

 You see, neither anorthite nor albite are actually colored themselves. What  is happening is that the nano-scale layers of anorthite and albite are acting like prisms but on the scale of a single wavelength of light. This means that incoming white light is broken up into its various wavelength components and is selectively reflected back at specific angles. That is why the color can only be observed from certain viewing angles. Like the wings of a morpho butterfly the color of labradorite is not due to any intrinsic property of the material itself but because of the physical nano-scale structure of the actual material. This marvelous feat occurs completely naturally and without the intervention of human hands.

Labradorite sample from Ylämaa Finland. All photographs are released under the Creative Commons BY-NC-SA License.

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Mission Statement

This blog is a place to discover the world of mineralogy and mineral collecting. You might wonder why one would care about simple “stones.” Here you will learn why an appreciation for mineralogy can be one of the best ways to establish a connection with, and a love for, the natural world.

 Minerals give us the structures we live in, the soil to grow our food in, and the chemicals to power our modern industry. Indeed, everywhere you walk is supported by countless billions of tons of rock that are in turn composed of hundreds or thousands of constituent minerals. Without minerals life, and our very planet would not exist.

 But this can be said for many things. Can it not? How can something so ubiquitous and fundamental to our world be of any special interest? There is a reason, and that reason is that minerals can provide a view into the natural mathematical and geometric order of the universe. Nowhere else can such perfect views of natural symmetry and purity of form be seen in nature. Perfectly faceted geometric shapes that formed out of molten lava, atomically flawless monocrystals the size of an automobile, and beautifully transparent birefringent crystals that can be used for precision optics. These are just some of the things you can discover in the world of mineralogy.

 This blog will provide insight into mineralogy through high-resolution photographs, scientifically valid description, and subjective opinion on various mineral samples. I hope to be able to show the reader why a certain mineral is significant; not just that it is.  The key to having an appreciation for something is to understand what it is and where it comes from. Consequently each blog post will have a section concerning the origin of the mineral species. I will answer the what, where, why, and how for every mineral I describe.

 I hope that this blog helps fuel an appreciation for the mineral world. If I can encourage one person to get involved in mineral collecting or mineralogy I would consider that to be a success. Minerals embody the mathematical perfection of the natural world in a tangible and beautiful form. I wish to share this beauty with the entire world.