igneous

Granite Pegmatite with Tourmaline and Muscovite

Pegmatite (Feldspar: KAlSi3O8, Quartz: SiO2, Schorl: NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH))

Hardness: 6-7.5 (depending on mineral); Color: White to light grey matrix with black crystals; Luster: Vitreous to pearly; Structure: Macro-crystalline phaneritic; Cleavage: Perfect on mica, poor on quartz.

Hardness: 6-7
Color: White to light grey matrix with black crystals
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. Highly fluid, water-rich melts allow for the growth of exceptionally large crystals in intrusive igneous environments.

Uses & applications

Used in gemstone collection, mineral specimens for education, and industrial sources of rare elements like lithium, beryllium, and high-purity quartz/mica.

Geological facts

Pegmatites are famous for containing some of the largest crystals on Earth, sometimes reaching over 10 meters in length. This specimen specifically shows black schorl tourmaline embedded in a quartz-feldspar matrix.

Field identification & locations

Identify in the field by looking for unusually large grain sizes compared to surrounding granite. Found globally in continental shields like Brazil, Madagascar, and the Appalachian Mountains.

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