Origin of gem minerals. Cutaway artworks showing ways in which gem minerals can form. Shown here are two cross-sections through the Earth's continental crust to a depth of 40 kilometres. Gemstones form within the crust at different levels and at different temperatures. At right is molten magma (orange) rising from the depths, while at left is a mass of cooled intrusive rock (pink) and hydrothermal water (blue).
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