igneous

Pegmatite

Granitic Pegmatite

Hardness (Mohs scale): 6-7; Color: Pinkish-brown (feldspar), grey/clear (quartz), black (accessory minerals); Luster: Vitreous to pearly; Crystal structure: Very coarse-grained (phaneritic); Cleavage: Good in feldspar grains; Specific gravity: 2.6-2.7

Luster: Vitreous to pearly

Identified May 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed during the final stages of a magma's crystallization, usually in hydrothermal or intrusive environments where high water content allows for the growth of exceptionally large crystals. Most common in Precambrian or Paleozoic shields.

Uses & applications

Source of rare earth elements, industrial minerals like quartz and feldspar, and gemstones such as tourmaline, beryl, and spodumene.

Geological facts

Pegmatites are famous for holding the world's largest crystals; some spodumene and beryl crystals in pegmatites have been recorded at over 10 meters long.

Field identification & locations

Identify in the field by searching for exceptionally large, interlocking crystals of quartz and feldspar within granitic terrain. They often form dikes or veins cutting through smaller-grained igneous rocks.

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