A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks and occasionally organic materials that are not minerals are also used for jewelry and are therefore often considered to be gemstones as well. Rarity and notoriety...
A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks and occasionally organic materials that are not minerals are also used for jewelry and are therefore often considered to be gemstones as well. Rarity and notoriety are other characteristics that lend value to gemstones. Found all over the world, the industry of coloured gemstones is currently estimated to be around 10–12 billion US dollars. Apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem expert is a gemologist, a gem maker is called a lapidarist or gemcutter; a diamond cutter is called a diamantaire. The traditional classification in the West, which goes back to the ancient Greeks, begins with a distinction between precious and semi-precious; similar distinctions are made in other cultures. This distinction reflects the rarity of the respective stones in ancient times, as well as their quality: all are translucent with fine color in their purest forms, except for the colorless diamond, and very hard, with hardnesses of 8 to 10 on the Mohs scale. Use of the terms 'precious' and 'semi-precious' in a commercial context is, arguably, misleading in that it suggests certain stones are more valuable than others, when this is not reflected in the actual market value. In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the emerald , aquamarine , red beryl , goshenite , heliodor , and morganite , which are all varieties of the mineral species beryl. Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture and luster. Diamonds are graded using a system developed by the Gemological Institute of America in the early 1950s. Other gemstones are still graded using the naked eye . A mnemonic device, the "four Cs" , has been introduced to help describe the factors used to grade a diamond.