igneous

Pegmatite

Granitic Pegmatite

Very coarse-grained texture (crystals >1cm); Hardness: 6-7 (Mohs); Color: Mottled pink (orthoclase), white/gray (quartz), and black/silver (mica); Luster: Vitreous to pearly; Structure: Phaneritic/Pegmatitic.

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

Identified March 27, 2026More igneous →

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Physical properties

Formation & geological history

Formed during the final stage of a magma's crystallization. Highly fluid, water-rich melts allow for rapid ion movement, resulting in exceptionally large crystals. Most common in Precambrian or Paleozoic shields.

Uses & applications

Source of rare earth elements (lithium, cesium, tantalum), industrial minerals like feldspar and mica, and gemstones such as beryl or tourmaline.

Geological facts

Pegmatites are known for containing the largest crystals found on Earth; some spodumene crystals in South Dakota have reached 42 feet in length.

Field identification & locations

Identify by exceptionally large, interlocking crystals of quartz and pink feldspar. Commonly found in mountain ranges and tectonic belts. Collectors value pieces with well-defined crystal faces or rare accessory 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