igneous

Granite (with Muscovite Mica)

Phaneritic Felsic Igneous Rock (primarily Quartz SiO2, K-Feldspar KAlSi3O8, and Muscovite KAl2(AlSi3O10)(OH)2)

Hardness: 6-7 (Mohs); Color: White, grey, and pink base with silver/metallic flakes; Luster: Vitreous to pearly; Crystal structure: Phaneritic (coarse-grained); Cleavage: Perfect basal cleavage in the mica flakes.

Hardness: 6-7 (Mohs)
Color: White, grey, and pink base with silver/metallic flakes
Luster: Vitreous to pearly

Identified March 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep beneath the Earth's surface (plutonic). This crystallization process can take millions of years, typically occurring in continental crust environments during mountain-building events.

Uses & applications

Widely used in construction for countertops, floor tiles, and building veneers. The mica component was historically used as an insulator in electrical equipment and currently in cosmetics for shimmer.

Geological facts

The silver, reflective flakes visible in this specimen are Muscovite mica, often called 'Isinglass'. In ancient times, large sheets of this mica were used as window glass because of their transparency and heat resistance.

Field identification & locations

Identify in the field by its coarse 'salt and pepper' appearance and the presence of reflective, flaky sheets of mica. It is commonly found in batholiths and mountain ranges like the Sierra Nevada or the Appalachians.

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