Current thinking indicates that our planet, Terra, started life as a ball of white-hot gas, about 50 billion years ago.  As this gas cooled and condensed, the various elements were formed, and then gave rise to molecular combinations.  An atom of Silicon (the most common element in the Earth’s crust) combines with two atoms of Oxygen to form Silicon Dioxide, perhaps the single most common source of gems and crystals. 

Silicon Dioxide is the basic chemical composition of such crystals as Agate, Amethyst, Citrine, Quartz and a number of others.)

Various trace elements and compounds add color and texture to these stones.  Heat and other environmental conditions further add their effects.  Purple Amethyst and Yellow Citrine, for example, are chemically the same, with those forming in cooler temperatures remaining the deepest purple, while those exposed to progressively higher temperatures developed as lighter violets or turning yellow.  The stones called “Ametrine” actually developed with one side cool and the other side hot, so one sees the purple of the Amethyst in one end of a crystal and the yellow of the Citrine in the other.

Gems, crystals and common rocks generally fall into three categories:

1.                 Igneous rocks were formed in the molten mantle of our planet, born of volcanic magma and formed in fire.

2.                 Sedimentary rocks were formed from chemical “mud” which settled to the bottom of lakes and seas, then gradually hardened over the millennia.

3.                 Metamorphic rocks begin their development as sedimentary rocks, then are exposed to high pressure and heat and gradually change (metamorphose, hence the name) into something different.

All inorganic gems are formed in one of these ways, and all are crystalline with a fixed, geometric structure.  (Some may be cryptocrystalline, being made up of a composite of very tiny crystals, often not individually distinguishable with the naked eye.)  These may be found in rough form, or smoothed by wind or water action.  For use in jewelry, they typically are either shaped into smooth, round or oval shapes, flat on one side, known as cabochons, or cut and faceted in order to bring out the most of their crystalline beauty.  Usually, only the relatively clear or transparent stones are faceted, to maximize refraction of light within them.  Opaque stones, such as Malachite or Turquoise, for example, are rarely faceted.

Organic gems, however, are the products of living things.  These include Amber (Fossilized Plant Resin,) Pearls (produced by Oysters,) and Coral (the exoskeletons of living plant-like animal organisms in the sea.)  Coal, formed from ancient plants, is subjected to intense heat and pressure, turning first into coal, then Jet, then later, after even more heat and pressure, into diamonds.

It is ironic to think that even though we now know that heat plays an important part in the formation of many gemstones, the very name, “crystal,” comes from the Ancient Greek “crystallos,” meaning “frozen ice.”  Pliny, a great Roman natural historian, believed that crystals were formed in very high, very cold, places.  This theory didn’t die out for nearly 2,000 years, until the latter part of the 18^th Century.  It may have been attempts to thaw, or melt, crystals, which inadvertently led to the discovery that heat-treating some of them often changed their colors.