Understanding Gemstones

By Eric Hartwell


While most people think of gemstones as minerals, the fact is, they are not. Gemstones, by definition, are substances such as rocks (e.g. lapis lazuli or onyx), petrified substances such as amber (which is fossilized tree sap), minerals (diamonds or emeralds) and organically-grown substances (pearls or coral) that are either collectible (as in having or acquiring value) or used in jewelry.

Gemstones have traditionally been divided into precious (or ‘cardinal gems’) stones, classified as such through a combination of rarity, historical significance, or religious or ceremonial use, or semi-precious stones. Customarily, only five stones are called “precious” – diamonds, rubies, sapphires, emeralds and amethysts. In current usage, however, gemologists classify all stones as precious although – as George Orwell once put it, “some things are more equal than others” – some gemstones (especially sapphires, emeralds, rubies and diamonds) are considered more valuable than others.

Gemstones by Cut and Polish
Of the more than 2000 natural minerals identified, fewer than 100 are classified as gemstones, and of these, only 16 have gained any importance – and almost none of these are used in their natural state. All have to be cut and polished to enhance their beauty and features.

The two major classifications for cutting stones are as cabochons, which are dome-like, smooth stones (usually done to opaque stones such as opals, turquoise or onyx), and faceted (applied to ‘transparent’ stones, especially the five habitually classified as precious stones), where small ‘windows’ are cut in the stone at planned angles at regular intervals, which shows the stone’s optical properties to best advantage. Reflected light is maximized, being seen by the viewer as the sparkle which ‘separates’ the cardinal gems from everyone else. The faceting method is applied to ‘transparent’ gemstones like diamonds, emeralds and rubies.

This is part of the reason why the transparent gemstones like diamonds, rubies emeralds and sapphires are so expensive and valuable – great care and planning go into the cutting of the facets and the polishing of the stones. If the angles are too shallow or too steep – or placed at the wrong intervals – light passing through the stone will not be reflected back to the viewer, and the stone’s quality and value are negated.

Treatments Applied to Gemstones
Gemstones are sometimes subjected to various ‘treatments’ intended to enhance color quality or clarity. Among the standard treatments used are:

- Heating the stones, mostly aquamarine, sapphires and rubies, in order to improve their color and clarity. Aquamarine, for example, is heat-treated in order to remove yellows in order to bring out a purer blue.

- Radiation has also been applied to blue topaz, especially the lighter and darker shades to change the white color to an even blue. Some colorless diamonds have turned green, rose quartz turns brown and decolorized amethyst have turned back to their original rich purple. The downside to this treatment is that some color changes are not permanent – and the stone may become radioactive.

- “Waxing” emeralds and turquoise is a long-standing practice, intended to disguise the natural cracks that many of these stones have. The wax or oil used is often colored so as to enhance the stone’s clarity

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