igneous

Granodiorite

Granodiorite (containing Plagioclase, Quartz, and Biotite)

Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (light gray base with dark flecks). Luster: Phaneritic (crystalline/dull). Structure: Coarse-grained intrusive. Specific Gravity: 2.6-2.7.

Hardness: 6-7 on Mohs scale
Color: Salt-and-pepper (light gray base with dark flecks)
Luster: Phaneritic (crystalline/dull)

Identified March 18, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (light gray base with dark flecks). Luster: Phaneritic (crystalline/dull). Structure: Coarse-grained intrusive. Specific Gravity: 2.6-2.7.

Formation & geological history

Formed through the slow cooling of silica-rich magma deep underground (plutonic). Found in batholiths and continental crust, typically dating from the Archean to the Cenozoic era.

Uses & applications

Used primarily in heavy construction, road building (crushed stone), and as ornamental stone for countertops or monuments (often sold commercially as "granite").

Geological facts

Granodiorite is the rock that makes up the famous Rosetta Stone. It is the most common rock type in the Sierra Nevada mountains of the United States.

Field identification & locations

Identify by its 'salt and pepper' appearance with more white/gray plagioclase than pink potassium feldspar. Commonly found in mountainous regions. Collectors look for large, distinct biotite or hornblende inclusions.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral