igneous

Granodiorite

Granodiorite (Intermediate intrusive igneous rock)

Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (mottled gray, white, and black); Luster: Phaneritic (crystalline/vitreous); Crystal Structure: Granular/Massive; Cleavage: None (though constituent minerals like mica and feldspar have it); Specific Gravity: 2.6–2.73

Hardness: 6-7 on Mohs scale
Color: Salt-and-pepper (mottled gray, white, and black)
Luster: Phaneritic (crystalline/vitreous)

Identified April 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma beneath the Earth's surface (plutonic). It is intermediate in composition between granite and diorite. Often associated with volcanic arc roots and mountain-building subduction zones.

Uses & applications

Used primarily in construction as crushed stone for road base, concrete, and railroad ballast. When polished, it is used for countertops, floor tiles, and ornamental building stone.

Geological facts

Many of the famous monoliths in Yosemite National Park, such as Half Dome, are composed largely of granodiorite rather than true granite. It contains more plagioclase feldspar than orthoclase feldspar.

Field identification & locations

Identify by its coarse-grained 'salt-and-pepper' appearance. Unlike granite, it appears darker due to a higher percentage of mafic minerals (biotite/hornblende). It is commonly found in large batholiths in the Sierra Nevada or the Cascades.

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