igneous

Granitic Pegmatite

Phaneritic Granite with Potassium Feldspar (KAlSi3O8), Quartz (SiO2), and Plagioclase

Hardness: 6-7 (Mohs scale); Color: Mottled pink, grey, and white; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Two directions at 90 degrees in feldspar; Specific gravity: 2.6-2.7.

Hardness: 6-7 (Mohs scale)
Color: Mottled pink, grey, and white
Luster: Vitreous to pearly

Identified March 21, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling and crystallization of magma deep beneath the Earth's surface during the final stages of a magma chamber's crystallization. Commonly associated with tectonic plate boundaries or ancient continental shields.

Uses & applications

Used primarily in construction as crushed stone for road base or architectural building stone. High-quality pieces are used for countertops or as sources for industrial crystals (quartz/feldspar).

Geological facts

Pegmatites are famous for containing exceptionally large crystals, sometimes reaching several meters in length, due to the high water content in the magma lowering viscosity during formation.

Field identification & locations

Identify in the field by its very large (over 1cm) interlocking crystals and distinct pink color from orthoclase feldspar. Common in mountainous regions like the Appalachians, Rockies, or Canadian Shield. Collectors look for accessory minerals like tourmaline or beryl.

Other igneous specimens

See all

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