Imagine ancient people coming upon a stone like none other; one that sparkles, has mesmerizing transparency and color and a naturally occurring geometric shape. Crystals and gems, long before being named or classified, gave such an impression as to make one assume they had been placed on this earth by the gods themselves. No wonder they were assigned magical and healing properties.
With the exception of pearls, amber and opal, nearly all gems are of crystalline origin. In fact, gems are “flawed” crystals. The atomic structure of crystals is such that they allow light to pass through. It is impurities caught inside crystals, and that absorb light instead of allowing it through, that cause the beautiful colors of gems. “Impurity,” in this case, is taken quite literally as a component that is not of pure, crystalline origin. A gem, then, is that part of a crystal that shows deep color.
The “impurities” are actually trace minerals. The most common trace minerals that are responsible for the occurrence of what we call gem are copper, iron, manganese, titanium and chromium.
Here are some examples of how they affect color and turn parts of crystals into gemstones: Sapphire, garnet and peridot are produced due to the presence of iron. Chromium is responsible for the ruby. Copper is the cause of the blue-green turquoise. Notice that crystals are composed of various minerals themselves. A corundum based crystal is colorless when it does not contain impurities. Add titanium and it is blue sapphire; add chromium and it becomes a red ruby. The process takes millennia.
A crystal, or a portion thereof, is deemed to be a gemstone based on the presence of color generating minerals within and on the quality of that color.
And that’s what makes a gem… in a nutshell!