Most consumers are familiar with precious and semi-precious jewels, but there are numerous other classifications of gems and stones.
Gemstones are divided into two categories: precious and semi-precious, and there are only four types of precious gems--diamond, emerald, ruby and sapphire. Semi-precious examples include, but are not limited to, agate, aquamarine, hematite, citrine, quartz, topaz, turquoise and opal.
Gemstones can be broken down into three basic categories: crystalline versus amorphous, organic versus inorganic and mineral versus rock. Crystalline gems are made of a single crystal like a diamond or a ruby, and they come from a single element like the carbon a diamond contains. Amorphous stones are made of different substances. The components can be crystals, but the gem itself is not a single crystal--turquoise, for example. Organic rocks are composed of material that was once a living organism or associated with one. For example, amber is fossilized tree sap and pearls come from oysters. Inorganic stones come from nonliving material--examples include rubies, emeralds and amethysts. Minerals are a singular material created through geological processes. Diamonds, rubies and jade are in this category. Rocks are composed of numerous minerals. An example is lapis lazuli.
Gems can be further categorized according to their chemical composition, their crystal structure, optical characteristics, color and durability. Chemical composition refers to stones that are composed of pure or compound elements. The manner in which the parts of a crystal line up next to each other determines its crystal structure classification. Optical characteristics are the result of a gem's chemical composition and crystal structure. In simple terms, it refers to the way a stone looks and how it refracts light. Color is the result of absorption or transmission of light. It is defined in terms of hue, tone and intensity. In geology, durability refers to a stone's hardness.
Manufactured stones are designed to imitate natural stones. An example is cubic zirconia, a synthetic diamond made from zirconium oxide. It has neither the chemical composition nor the physical characteristics of the real thing.
In addition to jewelry, stones of all types have other uses. Diamonds, for example, are used for certain saw blades, for their strength. Astrology associates specific stones with certain birth signs. Practitioners of nature religions such as Wicca and Paganism assign magical properties to various stones. In this tradition, certain associations are standard: • Diamonds are a symbol of purity, an amplifier of energy, and are said to treat eyesight problems. • Emeralds are stones of inspiration and patience. They are believed to aid in recovery after infections and to treat everything from the sinuses and lungs to the heart, spine and muscles. • Quartz crystals are readily obtained. They are said to be the most powerful healing and energy amplifier because of the way they are shaped. Quartz stimulates the immune system and balances the body. • Turquoise is believed to be a powerful healer of both the body and the mind and to change color to warn of the danger of infidelity.