igneous

Granite

Granite (Mainly Quartz SiO2, K-Feldspar KAlSi3O8, and Plagioclase)

Hardness: 6-7 (Mohs scale); Color: Mottled pink, white, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained, visible interlocking crystals); Cleavage: Indistinct on rock, perfect on individual feldspar grains; Specific gravity: 2.63 - 2.75.

Hardness: 6-7 (Mohs scale)
Color: Mottled pink, white, and black
Luster: Vitreous to dull

Identified April 11, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below Earth's surface (intrusive). The visible grains indicate a slow cooling process over thousands to millions of years. It is found in continental crust and often dates to various eras, frequently forming the basement rock of continents.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. Also popular as a collector specimen for teaching petrology.

Geological facts

Granite is one of the hardest and oldest rocks on Earth; some samples are nearly 4 billion years old. It makes up a large portion of the continental crust and forms the core of many major mountain ranges like the Himalayas and the Rockies.

Field identification & locations

Identify in the field by its 'salt and pepper' or mottled appearance and the presence of visible mica (shiny flakes), quartz (clear/grey glassy areas), and feldspar (opaque blocky crystals). It is commonly found in mountain outcrops, river beds, and glacial till.

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