igneous

Granitic Pegmatite

Granitic Pegmatite (principally Quartz, Potassium Feldspar, and Mica)

Hardness: 6-7 (Mohs scale); Color: Pinkish-tan (feldspar), smoky gray/white (quartz), black (mica); Luster: Vitreous to pearly; Crystal structure: Very large, interlocking crystals (phaneritic/pegmatitic texture); Cleavage: Perfect in feldspar and micas.

Hardness: 6-7 (Mohs scale)
Luster: Vitreous to pearly

Identified April 8, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the final, water-rich stages of a cooling magma chamber deep within the Earth's crust. The high water content allows for rapid ion diffusion, creating exceptionally large crystals.

Uses & applications

Source of rare earth elements, gems (like tourmaline or beryl), feldspar for ceramics, and quartz for glass. High-quality samples are used as geological specimens.

Geological facts

Pegmatites are famous for containing the largest crystals ever found on Earth, with some individual crystals reaching several meters in length. They are essentially 'giant-grained' granite.

Field identification & locations

Identify in the field by the unusually large size of the individual mineral grains (usually >1cm). Commonly found in the cores of mountain ranges or within metamorphic shields.

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