igneous

Granodiorite

Granodiorite (intermediate plutonic rock)

Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (gray/white with black speckles). Luster: Phaneritic (crystalline). Crystal structure: Coarse-grained granular. Cleavage: Non-existent in the rock mass, but present in individual mineral grains like feldspar. Specific Gravity: 2.6-2.7.

Hardness: 6-7 on Mohs scale
Color: Salt-and-pepper (gray/white with black speckles)
Luster: Phaneritic (crystalline)

Identified April 10, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of silica-rich magma deep within the Earth's crust (plutonic). It is typically found in volcanic arcs and mountain-building regions. Age can range from Precambrian to Cenozoic depending on the specific batholith.

Uses & applications

Predominantly used as crushed stone for road construction, railroad ballast, and building foundations. Also used for architectural facing, monuments, and curbing.

Geological facts

The famous Rosetta Stone is actually carved from granodiorite, not basalt as was originally thought for many years. It is intermediate in composition between granite and diorite.

Field identification & locations

Identify in the field by its phaneritic (visible grains) texture and the high proportion of plagioclase feldspar over orthoclase. Look for speckling of biotite or hornblende. It is very common in large batholiths 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