igneous

Granite

Phaneritic Intrusive Igneous Rock (composed of Quartz, Feldspar, and Mica)

Hardness: 6-7 Mohs; Color: Gray, pink, white, with black specks; Luster: Dull to pearly (vitreous on mineral faces); Crystal Structure: Phaneritic (coarse-grained); Cleavage: None (rock breaks unevenly); Specific Gravity: 2.63 - 2.75

Hardness: 6-7 Mohs
Color: Gray, pink, white, with black specks
Luster: Dull to pearly (vitreous on mineral faces)

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep underground. This slow cooling allows for large, visible crystals to form. It can date back to any geological age where continental crust was forming, notably during the Precambrian and Paleozoic eras.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, and monuments due to its durability and aesthetic appeal. Also used as crushed stone in roadbeds and concrete.

Geological facts

Granite makes up the majority of Earth's continental crust. Mount Rushmore is carved into a massive granite batholith in South Dakota, and the rock's density makes it resistant to weathering over thousands of years.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals. It is commonly found in mountain ranges (batholiths) and shields. For collectors, look for samples with larger crystals or unusual coloration from high orthoclase feldspar content.

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