Minerals are pure substances found in nature. Rocks are made up of one or more
A gemstone or semi-precious stone, is a piece of attractive mineral, which when cut and polished is used to make jewelry or displayed as a collector item.
There are also organic materials such as amber or lapis-lazuli that are still used for jewelry although they are not minerals, and they are also considered gemstones.
Most gemstonesgemstones are hard (above 7 on the Mohs table of hardness). The harder the stone, the better polish it can take. Softer minerals are also used in jewelry because of their aesthetic value. The rarity of a rock specimen also lends to the value of the gemstone.
Gemstones are clasified into precious and semi-precious stones. This distinction goes back to the Ancient Greeks and it reflects the rarity as well as the quality of the stone.
Because such a definition can change over time and vary with culture, it has always been a difficult matter to determine what constitutes precious stones.
The precious stones are diamond, ruby, emerald and sapphire. All other gemstones are classified as semi-precious.
There are other modern distinctions such as the one that is based on the color, translucency and hardness. Using the terms 'precious' and 'semi-precious' could be somewhat misleading.
Today, gemstones are identified by gemologists according to their characteristics such as chemical composition, crystal system and habit (the form the stone is found in).
Inclusions are different materials or flaws present in a specific stone.
Only diamonds have a universally accepted grading system. The "four C's" (color, cut, clarity and carat), has been introduced to help the consumer understand the factors used to grade a diamond.
These categories can be useful in grading other gemstones as well. In such case the four criteria will carry different weights. While in diamonds the cut comes first followed by clarity and color, a gemstone quality is determined primarily by color (the purity and beauty of it) followed by clarity and cut.
Prices of gems can fluctuate quite heavily, unlike the prices of diamonds which are quite stable.