igneous
Pegmatite with quartz, feldspar, mica, and tourmaline
Granitic pegmatite; chiefly quartz (SiO₂), feldspar, muscovite, and black schorl tourmaline (NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄)
AI-generated identification · may be incorrectCoarse-grained, with white blocky feldspar, translucent gray-brown quartz, shiny black tourmaline, and possible mica. Quartz hardness is 7, feldspar 6–6.5, tourmaline 7–7.5; luster is glassy to pearly, and feldspar shows cleavage.
Identified More igneous →
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Physical properties
Coarse-grained, with white blocky feldspar, translucent gray-brown quartz, shiny black tourmaline, and possible mica. Quartz hardness is 7, feldspar 6–6.5, tourmaline 7–7.5; luster is glassy to pearly, and feldspar shows cleavage.
Formation & geological history
Formed when volatile-rich granitic magma cooled slowly in late-stage veins, allowing unusually large crystals to grow. Most pegmatites are Precambrian to Mesozoic, though their exact age requires locality information.
Uses & applications
Used as a collectible mineral specimen; pegmatites are also sources of feldspar, quartz, mica, lithium, tantalum, and gem tourmaline, but this piece is not typically a construction stone.
Geological facts
The black crystals are likely schorl tourmaline, commonly forming prismatic or radiating aggregates in pegmatites. The brown translucent material may be smoky quartz or iron-stained quartz.
Field identification & locations
Identify it by its extremely coarse interlocking crystals, white feldspar, glassy quartz, and black tourmaline. Common localities include Maine, California, Brazil, Madagascar, and Afghanistan; a specific locality would improve identification.
