igneous

Granitic Pegmatite

Granitic Pegmatite with Quartz and Feldspar

Hardness: 6-7 (Mohs scale), Color: tan, white, and translucent, Luster: vitreous to pearly, Structure: phaneritic/very coarse-grained crystals, Cleavage: good (in feldspars), Specific Gravity: ~2.6.

Identified April 3, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs scale), Color: tan, white, and translucent, Luster: vitreous to pearly, Structure: phaneritic/very coarse-grained crystals, Cleavage: good (in feldspars), Specific Gravity: ~2.6.

Formation & geological history

Formed from the final, water-rich stages of a magma's crystallization. The high water content allows ions to move quickly, forming exceptionally large crystals. These are typically found in batholiths and surrounding metamorphic rocks.

Uses & applications

Source of high-purity quartz and feldspar for glass/ceramics; some yield rare earth elements and gems like tourmaline or beryl. Often used as decorative stone.

Geological facts

Pegmatites can host the largest crystals known on Earth, sometimes reaching over 10 meters in length. They are the 'garbage cans' of magmatic systems, concentrating rare elements like Lithium, Beryllium, and Tantalum.

Field identification & locations

Identify by exceptionally large crystal size compared to the surrounding rock. Common in geologically old continental crust areas like the Appalachians or the Black Hills. In the field, look for sparkling mica flakes and glassy quartz veins.

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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