igneous

Granodiorite

Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled grey, white, and black); Luster: Phaneritic/Crystalline; Crystal Structure: Coarse-grained intrusive; Specific Gravity: 2.6-2.73.

Hardness: 6-7 (Mohs scale)
Color: Salt and pepper (mottled grey, white, and black)
Luster: Phaneritic/Crystalline

Identified April 4, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled grey, white, and black); Luster: Phaneritic/Crystalline; Crystal Structure: Coarse-grained intrusive; Specific Gravity: 2.6-2.73.

Formation & geological history

Formed through the slow cooling of silica-rich magma deep underground. It is an intrusive igneous rock intermediate between granite and diorite, common in volcanic arcs and mountain roots.

Uses & applications

Used widely in construction as crushed stone for road base, building stone (similar to granite), countertops, and pavers. It is valued for its durability and aesthetic similarity to granite.

Geological facts

Granodiorite is the rock type that makes up the famous Rosetta Stone. It is also a primary component of the continental crust and forms large batholiths like those in the Sierra Nevada mountains.

Field identification & locations

Identify in the field by its coarse-grained 'salt and pepper' appearance and high presence of plagioclase feldspar over alkali feldspar. It is commonly found in large mountain ranges formed by tectonic subduction.

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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