igneous

Granitic Pegmatite

Granite Pegmatite (coarse-grained intrusive igneous rock)

Hardness: 6-7 (Mohs); Color: White to light grey matrix with black tourmaline/biotite inclusions; Luster: Vitreous to pearly; Crystal structure: Macro-crystalline (phaneritic); Specific Gravity: 2.6-2.7

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

Identified March 4, 2026More igneous →

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Physical properties

Formation & geological history

Formed during the final stages of a magma's crystallization, where high water content allows for the growth of exceptionally large crystals. Typically found in batholiths or dikes.

Uses & applications

Source of rare earth elements, industrial minerals like feldspar and mica, and host rock for gemstones such as tourmaline, beryl, and spodumene.

Geological facts

Pegmatites contains the largest crystals ever recorded on Earth, sometimes reaching over 10 meters in length. This specimen specifically shows Schorl (black tourmaline) embedded in a quartz/feldspar matrix.

Field identification & locations

Identify by the unusually large grain size compared to normal granite and the presence of accessor minerals like black tourmaline. Commonly found in mountainous regions with ancient crystalline basement rocks like the Appalachians or the Black Hills.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral