igneous

Granitic Pegmatite

Coarse-grained Igneous Rock (Granitic composition: KAlSi3O8, SiO2)

Hardness: 6-7 (Mohs scale); Color: Mottled white, cream, and black; Luster: Vitreous to pearly; Crystal structure: Macro-crystalline (very large crystals); Cleavage: Perfect in feldspar, none in quartz; Specific gravity: 2.6-2.7

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

Identified March 26, 2026More igneous →

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Physical properties

Formation & geological history

Formed during the final stage of magma crystallization where high water content allows for rapid ion migration and massive crystal growth. Typically found in late-stage intrusive plutons or as dikes/veins.

Uses & applications

Used as a primary source for rare-earth elements, industrial minerals like mica and feldspar, and occasionally as structural stone or architectural slabs.

Geological facts

Pegmatites are famous for hosting the world's largest crystals; some spodumene crystals in pegmatites have reached lengths of 40 feet. They are also the primary source of many gemstones like tourmaline and beryl.

Field identification & locations

Identify in the field by looking for exceptionally large intergrown crystals of quartz and feldspar exceeding 1 cm. Common in mountain ranges and ancient shields. Collectors should look for 'pockets' within the rock which may contain high-quality crystals.

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

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral