Friday, June 22, 2012

Mineral vs. Rock vs. Gemstone vs. Crystal

[13th century crosier, a stylized staff used in Christianity, carved from rock crystal (clear quartz).]     

The words mineral, rock, stone, gem, gemstone, and crystal are often used interchangeably but each has specific meanings.


The word mineral comes from the Latin minerale (“obtained by mining”). In geology, a mineral is a naturally occurring solid substance. Each has a specific chemical composition, made of either one or more elements, arranged in a regular three dimensional pattern, producing a crystal structure.  Some minerals do not meet all three criteria, lacking a crystal structure, like liquid mercury.  They are called mineraloids instead.  This category may also includes materials produced by an organic process, like amber, jet, and pearl.


Rock and stone are often used interchangeably in American English but they have different meanings historically. Both words come from Old English. Rock meant something large, like a rock formation, and stone meant something smaller, often transformed by human hands, like a millstone, tombstone, or gemstone.  This distinction still remains in British English.

In geology, a rock is a material made up of two or more minerals. For example, pyrite is a mineral but lapis lazuli is a rock, a combination of golden pyrite, blue lazurite, and white calcite.


The word gemstone comes from the Old English gimstan, combining the Latin gemma (“a precious stone, a leaf bud”) and the Old English stan (“a small rock, a stone shaped for a particular purpose”). Gemstones are valuable minerals and rocks that are rare, durable, and have distinctive color or clarity. However, lists of gemstones are very subjective, changing over time. Organic substances like amber, coral, and pearl may also be included. Diamond, emerald, ruby, and sapphire are historically called “precious gemstones” and others, “semi-precious”.  Amethyst was once considered precious until the vast deposits of Brazil lowered its monetary values.


The meaning of crystal has changed over time:

A: Quartz: The word crystal comes from the Greek krystallos (“ice, frost, crystal”). The ancient Greeks theorized that quartz was a petrified form of ice, since it was water clear, cool to the touch, and resembled an icicle. Its alternative name rock crystal reflects this etymology.

B: Colorless Glass: From antiquity to the late 19th century, quartz was a luxury item, often carved into vessels like pitchers, along with other semi-precious stones. Because these objects were so expensive, both labor intensive and wasteful of materials, imitations in glass developed. During the 15th century, Venetian glass makers produced an incredibly popular faux quartz called cristallo (Italian, “crystal glass”). Since then, high quality colorless glass has also been called crystal.

C: The Structure of Minerals: During the 17th and 18th century, the chemical patterns that produce minerals began to be studied scientifically. Because the geometric nature of quartz is clearly visible, they were named crystal structures, after it. In geology, a crystal is a substance with a regular shape, due to the repeating internal structure of its atoms.
© 2012, C. L. Matthews
[Image Source: Public domain, Wikipedia Commons]

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