A gemstone or gem is a piece of mineral crystal, which, in cut and polished form, is used to make jewelry or other adornments.
The most popular example of gemstone are Diamonds
Nearly all gemstones are formed beneath the Earth's surface. The process involved in the creation of the different stones can vary greatly. Many stones are formed when minerals react with the water that is near the Earth's surface and then dissolve. When this solution evaporates or cools, minerals form. Water that mixes with silica-rich rocks such as sandstone will produce gemstones such as amethysts, agates and opals.
Other gemstones such as emeralds and tourmalines are formed when rain water or water from cooling bodies of magma mix with minerals and then crystallize in open cracks or cavities. These spaces become filled with veins of minerals to create what is called hydrothermal deposits.
Diamonds are sometimes formed in metamorphic rocks although this process is rare. Most diamonds come from volcanic rocks called kimberlite. These rocks are named after the South African town of Kimberley where they were first discovered. Each ton of rock will only produce a few carats of diamond. In fact, the stone in a regular diamond ring will require the removal of 200 to 400 times its volume of rock!
