What is a gemstone?
A gemstone is a mineral or combination of minerals in crystal form which, when cut and polished 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. Other names used are gem, fine gem, jewel, precious stone, or semi-precious stone. Glass is not a gemstone obviously, but it can be fairly tricky to differentiate the two sometimes. Crystal, a form of lead glass, is also not a gemstone. It is a man-made gem using quartz, sand, and minerals.
The traditional classification begins by distinguishing between precious and semi-precious. The accepted modern classification states that precious stones are only four. Diamond, ruby, sapphire and emerald, with all other gemstones being semi-precious. This distinction reflects rarity above all. All are translucent with fine color in their purest forms, except for the colorless diamond (diamonds can be any color on the spectrum including the rare and very expensive black variety ).
Physical characteristics that make a colored stone valuable are color, clarity to a lesser extent (emeralds will always have a number of inclusions), cut, unusual optical phenomena within the stone such as color zoning (the uneven distribution of coloring within a gem) and asteria (star effects).
Many combinations of different gemstones are used in even the most expensive jewelry, depending on the brand name of the designer, and or fashion trends.
Recently in Artisan Jewelry, rough diamonds and other rough stones are being used coining the term Rough Lux.