metamorphic
Quartz with Mica (Gneissic or Pegmatitic origin)
Silicon Dioxide (SiO2) with Phyllosilicates (KAl2(AlSi3O10)(F,OH)2)
Hardness: 7 (Quartz) to 2.5 (Mica); Color: Milky white to tan with black/dark grey bands; Luster: Vitreous to pearly; Crystal structure: Hexagonal/Trigonal (Quartz) and Monoclinic (Mica); Cleavage: Conchonidal for quartz, basal for mica.
- Hardness
- 7 (Quartz) to 2
- Color
- Milky white to tan with black/dark grey bands
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 7 (Quartz) to 2.5 (Mica); Color: Milky white to tan with black/dark grey bands; Luster: Vitreous to pearly; Crystal structure: Hexagonal/Trigonal (Quartz) and Monoclinic (Mica); Cleavage: Conchonidal for quartz, basal for mica.
Formation & geological history
Formed through high-grade regional metamorphism or from late-stage igneous cooling in pegmatites. These structures are often found in Precambrian or Paleozoic crystalline basements where extreme heat and pressure cause the segregation of minerals.
Uses & applications
Used primarily as decorative stone, in construction as crushed aggregate, or as mineral specimens for education. Quartz has industrial uses in glass and electronics, while mica is used in insulation.
Geological facts
Quartz is the second most abundant mineral in Earth's continental crust. When found in bands like this, it often tells a story of tectonic movement and the deformation of the Earth's crust over millions of years.
Field identification & locations
Identify in the field by checking that the white parts cannot be scratched by steel (quartz hardness) and looking for the characteristic 'flaking' or shiny scales of the dark mica bands. Found commonly in mountainous regions or shield areas like the Appalachians or the Canadian Shield.
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