igneous
Quartz-bearing pegmatite specimen
Quartz (SiO₂) with feldspar and mica, likely granitic pegmatite
AI-generated identification · may be incorrectHardness: quartz 7, feldspar 6–6.5, mica 2–3; translucent white to gray, with vitreous quartz luster and blocky or flaky crystals. The coarse interlocking texture suggests pegmatite; exact identification is limited by the photograph.
- Hardness
- quartz 7, feldspar 6–6
Identified More igneous →
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Physical properties
Hardness: quartz 7, feldspar 6–6.5, mica 2–3; translucent white to gray, with vitreous quartz luster and blocky or flaky crystals. The coarse interlocking texture suggests pegmatite; exact identification is limited by the photograph.
Formation & geological history
Formed when water-rich, silica-rich magma cooled slowly in a late-stage igneous vein, allowing exceptionally large crystals to grow. Such pegmatites are commonly Precambrian to Phanerozoic in age and occur in continental crust.
Uses & applications
Quartz and feldspar are used in glass, ceramics, abrasives, and electronics; attractive pieces are sold as mineral specimens. This example appears to have modest collector value unless larger, cleaner crystals or rare accessory minerals are present.
Geological facts
Quartz commonly shows irregular fracture rather than cleavage, while feldspar has two good cleavage directions and mica splits into thin sheets. The brown material may be iron-stained feldspar, mica, or weathered accessory minerals.
Field identification & locations
Look for glassy, hard, translucent grains intergrown with opaque white feldspar and shiny flaky mica; quartz will scratch ordinary glass. Common localities include Brazil, Madagascar, the United States, and other granitic regions.
