igneous

Granite

Phaneritic Intrusive Igneous Rock (primarily composed of SiO2, Al2O3, K2O, Na2O)

Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (white, grey, and black); Luster: Dull to Vitreous; Crystal Structure: Phaneritic (coarse-grained, visible crystals); Cleavage: None (it fractures unevenly); Specific Gravity: 2.63 to 2.75

Hardness: 6-7 on Mohs scale
Color: Salt-and-pepper (white, grey, and black)
Luster: Dull to Vitreous

Identified March 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface (plutonic). It is found in large masses known as batholiths which form the core of many mountain ranges. Most granite dates from the Precambrian to Cenozoic eras.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. Due to its durability and aesthetic appeal, it is a primary material for architecture and interior design.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Mount Rushmore is carved into a granite batholith. It often contains trace amounts of radioactive elements like uranium and thorium, which can lead to the emission of radon gas.

Field identification & locations

Identify in the field by its 'salt and pepper' look where individual crystals of quartz (clear/grey), feldspar (white/pink), and mica or hornblende (black) are large enough to see with the naked eye. Found globally in continental shields and mountain belts. Collectors look for large, well-defined accessory minerals or unique colorations.

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