The relationship between gemstones and their formation environments

01 Gemstone formations from igneous rocks

Igneous rocks are rocks formed from the cooling and solidification of the magma deep within the Earth’s crust. In general, the longer and slower magma cools, the larger the resulting crystal formation will be. These long and slow crystallization processes often yield enormous crystals of gem-grade minerals, such as aquamarine, topaz, red beryl, tourmaline, citrine, amethyst, amazonite, spodumene, spessartine and feldspars. Igneous rocks also formed from some of the most valuable gemstones on Earth, including diamonds, pyropes, sapphires and olivines. These gemstones are crystallized deep within Earth’s mantle or in the lower sections of the Earth’s crust, and are embedded in rocks such as kimberlites, peridotites or basalts, and brought to the surface by magma eruptions.

Olivine in basalt Olivine


02 Gemstone formations from sedimentary rocks
Sedimentary rocks are formed from the accumulation, compaction and solidification of sediments from the weathering and erosion of rocks. Gemstones formed in sedimentary rocks are often secondary minerals, such as turquoise, opal, malachite, and chrysoprase. Most of these gemstones are produced within the fissures of sedimentary rocks.

Opal in limestone


03 Gemstone formations from metamorphic rocks
Rocks that have undergone internal structural or mineral changes as a result of external factors such as temperature, pressure or chemical environments are called metamorphic rocks. Some gemstones may be formed during the metamorphic processes; rubies, sapphires, spinels and cordierites can be found in marble with a high aluminum content; chrysoberyls, garnets and andalusites are found in schists with a high metamorphic degree; diopsides, epidotes and garnets can be found in contact metamorphic aureoles (regions of high temperature and low pressure); jade (jadeites) is formed in high pressure metamorphic environments.

Garnets in schist Manganese aluminum garnet



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