A gemstone also called a gem, fine gem, jewel, precious stone, or semi-precious stone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, and jade) or organic materials that are not minerals (such as amber, jet, and pearl) are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone.
Apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter; a diamond worker is a diamantaire. The carvings of Carl Fabergé are significant works in this tradition.
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. In modern use the precious stones are diamond, ruby, sapphire, and emerald, with all other gemstones being semi-precious. 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. Other stones are classified by their color, translucency and hardness. The traditional distinction does not necessarily reflect modern values, for example, while garnets are relatively inexpensive, a green garnet called tsavorite can be far more valuable than a mid-quality emerald. Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone. Use of the terms 'precious' and 'semi-precious' in a commercial context is, arguably, misleading in that it deceptively implies certain stones are intrinsically more valuable than others, which is not necessarily the case.
In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition. For example, diamonds are made of carbon (C) and rubies of aluminium oxide (Al2O3). Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in. For example, diamonds, which have a cubic crystal system, are often found as octahedrons.
Gemstones are classified into different groups, species, and varieties. 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 (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow), and morganite (pink), 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. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.
Material or flaws within a stone may be present as inclusions.
Gemstones may also be classified in terms of their "water". This is a recognized grading of the gem's luster, transparency, or "brilliance".Very transparent gems are considered "first water", while "second" or "third water" gems are those of a lesser transparency.
List of extremely rare gemstones
- Painitewas discovered in 1956 in Ohngaing in Myanmar. The mineral was named in honor of the British gemologist Arthur Charles Davy Pain. In 2005, painite was described by the Guinness Book of World Records as the rarest gem mineral on earth.
- Hibonitewas discovered in 1956 in Madagascar. It was named after the discoverer the French geologist Paul Hibon. Gem quality Hibonite has only been found in Myanmar.
- Red berylor bixbite was discovered in an area near Beaver, Utah in 1904 and named after the American mineralogist Maynard Bixby.
- Jeremejevitewas discovered in 1883 in Russia and named after its discoverer, Pawel Wladimirowich Jeremejew (1830–1899).
- Chambersitewas discovered in 1957 in Chambers County, Texas, USA, and named after the deposit's location.
- Taaffeitewas discovered in 1945. It was named after the discoverer, the Irish gemologist Count Edward Charles Richard Taaffe.
- Musgravitewas discovered in 1967 in the Musgrave Mountains in South Australia and named for the location.
- Grandidieritewas discovered by Antoine François Alfred Lacroix (1863–1948) in 1902 in Tuléar province, Madagascar. It was named in honor of the French naturalist and explorer Alfred Grandidier (1836–1912).
- Poudretteitewas discovered in 1965 at the Poudrette Quarry in Canada and named after the quarry's owners and operators, the Poudrette family.
- Serendibitewas discovered in Sri Lanka by Dunil Palitha Gunasekera in 1902 and named after Serendib, the old Arabic name for Sri Lanka.
- Zektzeritewas discovered by Bart Cannon in 1968 on Kangaroo Ridge near Washington Pass in Okanogan County, Washington, USA. The mineral was named in honor of mathematician and geologist Jack Zektzer, who presented the material for study in 1976.