igneous

Pegmatite

Granitic Pegmatite

Hardness: 6-7 (Mohs); Color: white, cream, tan, smoky gray with dark inclusions; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Good in feldspars, none in quartz; Specific gravity: 2.6-2.7

Hardness: 6-7 (Mohs)
Color: white, cream, tan, smoky gray with dark inclusions
Luster: Vitreous to pearly

Identified May 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed during the final stages of a magma chamber's crystallization when high water content allows for the growth of exceptionally large crystals. Most common in Precambrian and Paleozoic terrains.

Uses & applications

Source of rare earth elements, lithium (spodumene), gemstones like beryl, and industrial minerals like high-purity quartz and feldspar for ceramics and electronics.

Geological facts

Pegmatites are famous for producing the world's largest crystals, sometimes reaching several meters in length. They often contain rare minerals like tourmaline and lepidolite.

Field identification & locations

Identify by the large intergrown crystals of quartz, feldspar, and mica. Look for 'graphic' textures. Found globally in continental shields like the Black Hills (USA) or regions of Brazil.

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