Some gemstones have perfect crystalline structure, while others have none.
People often use the terms gemstone and crystal synonymously, when in fact the two words have very different definitions. Not all gemstones form crystalline shapes and not all crystals are gemstones. Some gemstones form crystals, however, and are most commonly seen in faceted form, which causes people to confuse the two terms.
Structure
Crystals are solid and have an ordered internal structure, typically forming smooth, flat faces. Crystals often form natural geometric shapes. A good example of a mineral that frequently forms crystals is quartz. Some gemstones, such as turquoise, opal, and amber, rarely or never form crystals. Faceted gemstones may appear to have a crystalline structure, but the facets are man-made.
Durability, Availability, and Appearance
Scientists identify gemstones based on the availability, durability, and beauty of the stone. Geologists classify the stones as "semi-precious" or "precious." Precious gemstones--such as diamonds, rubies, sapphires, and emeralds--are rarer than other gems. This means they are worth more than semi-precious stones such as amethyst, amber, and jade. Some substances form attractive crystals, but do not meet the other criteria for gemstones. Halite--or rock salt--forms crystals, but is not durable and widely available.
Uses
Gemstones are used to make jewelry or other ornamental items. Mineral crystals may have different uses based on their unique properties. For example, the gemstone amber, which is fossilized resin, has little use other than ornamental. Quartz crystals, however, are often a component in prisms, lenses, gauges, glass, paints, and abrasives, as well as jewelry.
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