igneous

Granodiorite (containing Biotite and Quartz)

Granodiorite (Plagioclase-rich phaneritic intrusive rock)

Hardness: 6-7 on Mohs scale; Color: Salt and pepper (mottled grey, black, and white); Luster: Vitreous to dull; Structure: Phaneritic (coarse-grained crystals); Cleavage: Distinct in feldspars, none in quartz.

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

Identified March 20, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of silica-rich magma beneath the Earth's surface (plutonic). Typically found in batholiths within continental crust and subduction zones.

Uses & applications

Used extensively in construction as 'granite' for countertops, paving stones, and road base construction. Also used in monumental architecture.

Geological facts

Granodiorite is the rock that makes up the famous Rosetta Stone. It is chemically transitional between granite and diorite, containing more plagioclase than orthoclase feldspar.

Field identification & locations

Identify in the field by its coarse crystalline texture where white/grey plagioclase exceeds pinkish orthoclase, mixed with black biotite or hornblende. Commonly found in mountain ranges like the Sierra Nevada.

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