igneous

Granite

Phaneritic Plutonic Rock (primarily Quartz, Feldspar, and Mica)

Hardness: 6-7 Mohs; Color: Mottled gray, black, and tan/pink; Luster: Vitreous to pearly; Crystal structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspar/mica, none in quartz; Specific gravity: 2.63 - 2.75

Hardness: 6-7 Mohs
Color: Mottled gray, black, and tan/pink
Luster: Vitreous to pearly

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling and crystallization of silica-rich magma deep within the Earth's crust. It is primarily found in continental crustal masses and can vary in age from millions to billions of years.

Uses & applications

Major construction material for countertops, floor tiles, and monuments. Also used as crushed stone for road base and railroad ballast. Well-crystallized specimens are sought after by geological collectors.

Geological facts

Granite is the most common rock in Earth's continental crust. Its large crystals are proof of slow cooling over tens of thousands of years. It is extremely durable, resistant to weathering, and can withstand high temperatures.

Field identification & locations

Identify by its 'salt and pepper' appearance and visible crystals of quartz (clear/gray), feldspar (tan/pink/white), and biotite or hornblende (black). It is found globally in mountainous regions and exposed batholiths. It does not react to acid.

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