igneous
Quartz-rich pegmatite
Granitic pegmatite; primarily quartz (SiO₂), with feldspar and mica, plus possible iron-oxide staining
AI-generated identification · may be incorrectTypically coarse-grained, with glassy to pearly luster, gray-clear quartz, pale feldspar, and reflective mica; quartz hardness 7, feldspar 6–6.5, mica 2–3. It has interlocking crystals, with mica showing prominent basal cleavage and quartz lacking cleavage.
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Physical properties
Typically coarse-grained, with glassy to pearly luster, gray-clear quartz, pale feldspar, and reflective mica; quartz hardness 7, feldspar 6–6.5, mica 2–3. It has interlocking crystals, with mica showing prominent basal cleavage and quartz lacking cleavage.
Formation & geological history
Forms when the final, water-rich melt of a granite crystallizes slowly in dikes or pockets, producing exceptionally large crystals. Most pegmatites formed during Precambrian to Phanerozoic mountain-building events, depending on locality.
Uses & applications
Used as an ornamental and teaching specimen; pegmatites may supply quartz, feldspar, mica, lithium, tantalum, beryl, and gemstones. This irregular matrix piece has limited jewelry value unless attractive gem crystals are present.
Geological facts
The sparkling flakes are likely muscovite or biotite, while rusty orange areas are iron oxides from weathering. Quartz can be confirmed by its hardness and lack of cleavage; feldspar commonly shows two cleavage planes near 90 degrees.
Field identification & locations
Common in granitic terrains worldwide, including Brazil, Madagascar, the United States, and Scandinavia. Estimated value: about $10–$50 for a common hand specimen, or $50–$200+ if it contains unusually large, well-formed crystals or collectible accessory minerals.
