Natural gemstones are minerals or stones that have not been artificially created. Often used for jewelry or ornamentation, they usually need to be polished and cut before they're considered gem-quality.
Many gems form deep in the crust and mantle of the Earth under extreme heat and pressure. These include diamonds and red garnets. The rocks containing these potential gems reach the surface either through uplift during mountain formation, mining operations, or magmas surging up from the earth. When magma reaches the Earth's surface as lava and cools, weathering can break it down and reveal the gems inside. This is why gems such as rubies and jade, although formed in the depths of the Earth, have been found in the Himalayas.
Gems also come from the upper part of the Earth's crust where the pressures are lower and the temperatures can vary. From here come gems such as garnet, andalusite and lapis lazuli.
During the last phase of granite crystallization, elements such as boron, beryllium and lithium can be concentrated. These elements form gems such as emerald, tourmaline and topaz.
Some types of gems don't come from inside the earth, but from living things. These include pearls, coral, amber and jet.