igneous

Quartz with Mica (Pegmatite)

Quartz (SiO2) and Muscovite (KAl2(AlSi3O10)(OH)2)

Hardness: 7 (Quartz) and 2-2.5 (Mica); Color: White, tan, and silvery; Luster: Vitreous to pearly; Crystal structure: Hexagonal and monoclinic; No cleavage in Quartz, perfect basal cleavage in Mica; Specific gravity: 2.65-2.8.

Hardness: 7 (Quartz) and 2-2
Color: White, tan, and silvery
Luster: Vitreous to pearly

Identified April 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed from late-stage cooling of magma in a pegmatite vein where high water content allows for large crystal growth. These structures often date back hundreds of millions to billions of years.

Uses & applications

Quartz is used in electronics (oscillators), glassmaking, and construction. Muscovite mica is used in insulation and as a glimmering agent in cosmetics.

Geological facts

Pegmatites are known for being the primary source of multi-colored gemstones and rare earth minerals because they concentrate elements that don't fit into earlier-forming crystals.

Field identification & locations

Identify in the field by the distinct combination of crystalline white quartz and the 'flaky' or 'platty' texture of mica that can be peeled with a fingernail. Often found in mountainous granitic regions.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral