igneous

Pegmatite (with Quartz and Feldspar)

Granitic Pegmatite

Hardness: 6-7 (Mohs scale); Color: Tan, white, and grey with orange-red iron staining; Luster: Vitreous to pearly; Crystal structure: Massive/large interlocking crystals; Cleavage: Perfect on feldspar grains, none on quartz grains; Specific Gravity: 2.5-2.8.

Hardness: 6-7 (Mohs scale)
Color: Tan, white, and grey with orange-red iron staining
Luster: Vitreous to pearly

Identified April 6, 2026More igneous →

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Physical properties

Formation & geological history

Formed during the final stages of a magma's crystallization. Highly fluid, water-rich magma allows for the growth of exceptionally large crystals. These are typically associated with large granitic intrusions and can date from billions of years ago to the Cenozoic era.

Uses & applications

Primary source of industrial minerals like quartz and feldspar (for glass and ceramics). It is also mined for rare elements (lithium, tantalum) and gemstones like tourmaline or beryl.

Geological facts

Pegmatites are famous for containing the world's largest individual crystals. Some beryl crystals in pegmatites have been recorded at over 14 meters (46 feet) in length.

Field identification & locations

Identify by exceptionally large grain size (usually >1cm). Look for interlocking translucent quartz and opaque feldspar. Commonly found in mountain belts and Precambrian shield areas. Use a scratch test to confirm hard minerals.

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

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral