igneous
Quartz-rich pegmatite with dark tourmaline
Quartz–feldspar pegmatite, likely with black schorl (tourmaline)
AI-generated identification · may be incorrectMostly white to cream, coarse crystalline quartz and feldspar with dark mineral patches. Quartz is Mohs 7, vitreous, and trigonal; feldspar is Mohs 6 with two cleavage directions; schorl is Mohs 7–7.5 and typically forms striated trigonal crystals.…
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Physical properties
Mostly white to cream, coarse crystalline quartz and feldspar with dark mineral patches. Quartz is Mohs 7, vitreous, and trigonal; feldspar is Mohs 6 with two cleavage directions; schorl is Mohs 7–7.5 and typically forms striated trigonal crystals. The specimen’s rounded shape may be weathered or collected from a stream.
Formation & geological history
Likely crystallized from water-rich residual granite magma in a pegmatite vein, where large crystals commonly form. Pegmatites occur across many geological ages; the image alone cannot establish this specimen’s age.
Uses & applications
Quartz and feldspar are used in glass and ceramics, while tourmaline is collected as a mineral and sometimes cut as a gemstone. This piece is mainly of modest collector interest.
Geological facts
Pegmatites can contain exceptionally large crystals and rare elements, although this specimen appears dominated by common quartz and feldspar.
Field identification & locations
Look for interlocking coarse white crystals and distinct black, often striated tourmaline; confirm with a fresh surface or mineral tests, since appearance alone is not definitive. Pegmatites are widespread, including in Brazil, the United States, and Madagascar.
