igneous

Granodiorite

Phaneritic-textured Intrusive Granodiorite

Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (mottled grey, white, and black); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained crystals visible to the naked eye); Specific gravity: 2.6 to 2.73.

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

Identified February 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of silica-rich magma deep within the Earth's crust (plutonic). It is common in continental crust and often found in mountain ranges formed by volcanic arcs. Geological age varies from Precambrian to Cenozoic depending on the specific batholith.

Uses & applications

Used widely as crushed stone for road construction and aggregate. High-quality slabs are used for countertops, building facades, and paving stones (often sold commercially as 'grey granite').

Geological facts

Granodiorite is the rock that makes up the famous Rosetta Stone and much of the Plymouth Rock. It is intermediate in composition between granite and diorite, containing more plagioclase feldspar than orthoclase feldspar.

Field identification & locations

Identify in the field by looking for a coarse grain size where white/grey plagioclase feldspar outnumbers pinkish orthoclase, mixed with dark biotite or hornblende. It is found in abundance in the Sierra Nevada mountains and other subduction zone cordilleras.

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

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral