igneous
Tourmaline-bearing pegmatite
Granitic pegmatite composed mainly of quartz, feldspar, mica, and schorl/elbaite tourmaline
AI-generated identification · may be incorrectCoarse-grained, irregularly intergrown crystals with pale quartz or feldspar and black-to-brown tourmaline; hardness is roughly 6–7 for quartz/feldspar and 7–7.5 for tourmaline, with vitreous to pearly luster. Individual minerals show uneven fracture, while feldspar may display cleavage.
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Physical properties
Coarse-grained, irregularly intergrown crystals with pale quartz or feldspar and black-to-brown tourmaline; hardness is roughly 6–7 for quartz/feldspar and 7–7.5 for tourmaline, with vitreous to pearly luster. Individual minerals show uneven fracture, while feldspar may display cleavage.
Formation & geological history
Formed when water-rich granitic magma crystallized slowly in a late-stage dike or pocket, allowing exceptionally large crystals; typically Precambrian to Phanerozoic depending on the pegmatite district.
Uses & applications
Collected as a specimen and mined for feldspar, quartz, mica, lithium, tantalum, beryllium, and gem tourmaline; attractive polished pieces may enter decorative or jewelry markets.
Geological facts
Pegmatites are among the world’s principal sources of rare elements and gemstones, including tourmaline, beryl, topaz, and spodumene.
Field identification & locations
Identify it by its very coarse texture, contrasting light quartz/feldspar and dark prismatic tourmaline, and non-layered igneous fabric; common in granitic terrains worldwide, notably Brazil, Afghanistan, Madagascar, and the United States.
