igneous

Granodiorite

Granodiorite (Intermediate intrusive igneous rock)

Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (light grey with dark speckles); Luster: Dull to vitreous; Crystal Structure: Phaneritic (coarse crystals visible to the naked eye); Cleavage: Dependent on mineral constituents (feldspar, quartz, biotite).

Hardness: 6-7 on Mohs scale
Color: Salt-and-pepper (light grey with dark speckles)
Luster: Dull to vitreous

Identified April 10, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of magma beneath the Earth's surface (intrusive). It is intermediate in composition between granite and diorite. Found in large batholiths often associated with mountain building events and subduction zones throughout geological history.

Uses & applications

Used extensively in construction as 'crushed stone' for road base and concrete. Higher quality slabs are used for architectural cladding, countertops, paving, and monuments.

Geological facts

Granodiorite is the rock type that makes up the famous Rosetta Stone. It is also the primary component of the Sierra Nevada batholith in California.

Field identification & locations

Identify in the field by its coarse-grained texture and balanced mix of light-colored plagioclase feldspar and dark minerals like biotite or hornblende. It contains more plagioclase than orthoclase, distinguishing it from true granite.

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