Igneous

Granitic Pegmatite

Granite Pegmatite (typically containing Quartz SiO2, Feldspar KAlSi3O8, and Muscovite)

Hardness (Mohs): 6-7; Color: Mottled white, tan, and brown/grey; Luster: Vitreous to pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Perfect in mica/feldspar components; Specific gravity: 2.6-2.7

Color: Mottled white, tan, and brown/grey
Luster: Vitreous to pearly

Identified March 8, 2026More igneous →

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Physical properties

Formation & geological history

Formed during the final stages of a magma's crystallization, usually in intrusive igneous environments. Water-rich fluids allow for the growth of very large crystals. These can date from the Archean to the Cenozoic era.

Uses & applications

Used as a source of rare earth elements, industrial minerals like mica and feldspar, and occasionally as structural stone or high-end countertops if found in large slabs.

Geological facts

Pegmatites are famous for containing the world's largest individual crystals, sometimes measuring several meters in length. They are the primary source of many gemstones like tourmaline, beryl, and topaz.

Field identification & locations

Identify by the exceptionally large crystal size relative to surrounding rocks (usually >1cm). Found in tectonic belts and near large granitic batholiths. Collectors look for 'vugs' or pockets containing well-formed 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