igneous

Granodiorite

Hardness: 6-7 on Mohs scale; Color: Gray to pinkish-gray with salt-and-pepper texture; Luster: Dull (weathered) to vitreous (fresh); Crystal Structure: Phaneritic (medium to coarse-grained); Cleavage: Dependent on mineral (feldspar/mica); Specific Gravity: 2.6-2.8

Hardness: 6-7 on Mohs scale
Color: Gray to pinkish-gray with salt-and-pepper texture
Luster: Dull (weathered) to vitreous (fresh)

Identified April 12, 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 (intrusive). They occur in large plutons or batholiths, often along convergent plate boundaries. Many are hundreds of millions of years old.

Uses & applications

Used widely as crushed stone for road construction, paving, and as architectural dimension stone (countertops, monuments) similar to 'commercial granite'.

Geological facts

Granodiorite is the rock that makes up the famous Rosetta Stone. It has a slightly higher concentration of dark minerals (biotite/hornblende) and plagioclase feldspar than true granite.

Field identification & locations

Identify by its interlocking crystalline texture and 'salt and pepper' appearance. Look for the presence of white/gray plagioclase, quartz, and dark specks of biotite or hornblende. It is common in mountain belts 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