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Some varieties of gems (including tourmalines, garnets, and beryls) form when pockets of water-rich magma cools and forms crystal masses called "pegmatites." Still others, particularly varieties of quartz gemstones, form during or after magma or lava cools and fractures in the cooling rock become locations where hot fluids (water and gases) release dissolved minerals to form crystal masses lining cavities in the host igneous rock. Some gems, like diamonds and peridote, melt at very high temperatures and can be transported by flowing magma (molten rock and gases) from sources deep in the earth, including the lower crust and mantle. This chapter examine selected common gemstones derived from rocks of igneous origin. Geology of Gems Chapter 6 - Gems From Igneous Rocks