Igneous/Metamorphic Hybrid
Quartz with Mica Schist (Pegmatite Specimen)
SiO2 (Silicon Dioxide) and Phyllosilicates (Biotite/Muscovite)
Hardness: 7 (Quartz) and 2-3 (Mica); Color: Milky white Quartz transition into dark brown/black Mica; Luster: Vitreous to pearly; Structure: Trigonal quartz with monoclinic plate-like mica; Cleavage: None (Quartz) to perfect basal (Mica).
- Hardness
- 7 (Quartz) and 2-3 (Mica)
- Color
- Milky white Quartz transition into dark brown/black Mica
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 7 (Quartz) and 2-3 (Mica); Color: Milky white Quartz transition into dark brown/black Mica; Luster: Vitreous to pearly; Structure: Trigonal quartz with monoclinic plate-like mica; Cleavage: None (Quartz) to perfect basal (Mica).
Formation & geological history
Formed in high-temperature pegmatite veins or contact metamorphic zones where magma interacts with existing country rock. Usually from the Proterozoic or Paleozoic eras in continental crust environments.
Uses & applications
Used in industry as a source of quartz for glass/silicon and mica for electrical insulation. Generally used as architectural stone or garden decoration; smaller pieces are sold as geological educational specimens.
Geological facts
Mica was historically used as window glass in furnace doors because of its extremely high heat resistance and transparency in thin sheets (known as Isinglass).
Field identification & locations
Identify in the field by the distinct transition from hard, glassy white quartz to flaky, dark brittle plates. Common in mountain ranges such as the Appalachians, Rockies, and Alpine regions.
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