Wednesday, September 15, 2010

Naming rocks, minerals, and gems

Rocks, minerals, and gems have a rich vocabulary. There seems to be only one naming rule: no uppercase letters. This might be intended to simplify the nomenclature, but it can be confusing when you encounter a name such as "childrenite." You assume that name was inspired by a child, but the name comes from an adult; J.G. Children. The practice of using lowercase for eponyms is different from anatomic nomenclatures, wherein capitalization is preserved (e.g., Eustachian tube, not eustachian tube, after Bartolomeo Eustachio).

Similarly, you would think that "greenockite" must be a green rock (it's most often yellow, not green). It gets its name from Lord Greenock.

Likewise, biotite does not derive from a biologic precursor. It's named after Jean Biot.

Contrarily, rocks are sometimes named for lowercase (common) nouns.

Sepiolite is named for the cuttlefish bone, sepia.

Serpentine is named after the snake.

Where rocks get names from people, it's usually the surname. But not always.

Torbernite is named for Torbern Olaf Bergmann (the given name).

But don't get carried away. Bruceite was not named after someone whose given name was Bruce. It was named for a surname (Archibald Bruce). Likewise, Vivianite was not named after a woman named Vivian. It also came from the surname: J.G. Vivian

Perhaps the final solution for naming rocks after mineralogists was solved with the naming of frankhawthorneite after Professor Frank Hawthorne, of the University of Manitoba.

Here are a few more surprises:

If a gem is given a name, you'd think that it must be distinguishable from other gems with different names. No. Sapphire and ruby are the same gem, with different colorations (due to impurities in the stone). They're color-variants of corundum. Similarly, amethyst is just a color variant (purple) of common quartz.

Color in a mineral's name can be highly misleading. Glaucodot (greek for "blue"), is a gray to white mineral; never blue. Glaucodot is, however, used in the manufacture of blue glass, but you'd never know that by looking at the mineral.

Some rocks are named after the place where it was discovered or mined.

For example bytownite is named for Bytown, the former name for what is now called Ottawa.

This can be confusing, as franklinite is not named for Ben Franklin. It's named for Franklin, New Jersey. The city was named for Ben Franklin, but not the rock.

Consider Trona, California, where trona (sodium bicarbonate, and variously called tron) is mined. The mineral was not named for the city. The city was named for the mineral, which took it's name from tron, a shortened form of natron, the Arabic word for sodium.

Some rocks are named for their taste:

Calomel (probably from ancient Greek, meaning honey-taste)

or odor:

Scorodite (garlic-like, in Greek)

Some rocks are named after their included elements.

Bismuthinite contains bismuth, as you would expect. Zincote (a zinc dispersion) contains zinc, as does zincite (a true mineral).


Zinkenite contains no zinc (named after JKL Zinken, a German mineralogist).

Similarly, selenite, a clear crystal form of gypsum, contains no selenium.

If you're interested in the names of rocks, you must really know your Latin. Septarian concretions have complex internal structures, with multiple branches. You might think that the term comes from the latin septem (seven) referring to the number of branches. You'd be wrong. The name comes from the latin septum (partition).

It's also good to know your mythology. Pollucite was named for Pollux, the twin of Castor. The name has a certain inevitability. Pollucite is often found alongside petalite, previously known as castorite.

Some rocks are named for their geometry. There's tetrahedrite (tetrahedral crystals), triplite, clinoclase, microcline, and anorthoclase. But you can never generalize in mineralogy. Anglesite is not named for the angles in the crystal. It's named for Anglesey, Wales, where it is mined.

Sometimes, the relationship between a rock and it's name can be the opposite of what you might imagine. Fluorite is a rock that fluoresces. You might imagine that it was named because it had the property of fluorescence. Wrong. Fluorite was named for fluorine, from which it is composed (CaF2). The mineral fluorite was found to change color under UV light. The phenomenon was called fluorescence, after the first mineral shown to produce the effect. Today, every mineral that changes it's emission color under UV light is said to be fluorescent, whether it contains fluorine or not.

Sometimes you're sure a rock's name has been misspelled. Surely goethite should be geothite. Alas, no. Goethite is named for the polymath Wolfgang van Goethe.

In summary, if you're interested in the semiotics of rocks, you (unlike the rocks) will need to be flexible.

- © 2010 Jules Berman tags: nomenclature, specification, geology, rocks and minerals, hobbyists, semiotics, logophiles

Science is not a collection of facts. Science is what facts teach us; what we can learn about our universe, and ourselves, by deductive thinking. From observations of the night sky, made without the aid of telescopes, we can deduce that the universe is expanding, that the universe is not infinitely old, and why black holes exist. Without resorting to experimentation or mathematical analysis, we can deduce that gravity is a curvature in space-time, that the particles that compose light have no mass, that there is a theoretical limit to the number of different elements in the universe, and that the earth is billions of years old. Likewise, simple observations on animals tell us much about the migration of continents, the evolutionary relationships among classes of animals, why the nuclei of cells contain our genetic material, why certain animals are long-lived, why the gestation period of humans is 9 months, and why some diseases are rare and other diseases are common. In “Armchair Science”, the reader is confronted with 129 scientific mysteries, in cosmology, particle physics, chemistry, biology, and medicine. Beginning with simple observations, step-by-step analyses guide the reader toward solutions that are sometimes startling, and always entertaining. “Armchair Science” is written for general readers who are curious about science, and who want to sharpen their deductive skills.