igneous

Granodiorite

Hardness: 6-7 on Mohs scale. Color: Light gray to salt-and-pepper. Luster: Dull to vitreous when crystals are fresh. Crystal Structure: Phaneritic (medium to coarse-grained). Composition: Quartz, Plagioclase feldspar, and minor Biotite/Hornblende.

Hardness: 6-7 on Mohs scale
Color: Light gray to salt-and-pepper
Luster: Dull to vitreous when crystals are fresh

Identified April 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep within the Earth's crust (plutonic). It is a major component of batholiths and continental crust, often dating from the Precambrian to Cenozoic eras.

Uses & applications

Used extensively in construction as crushed stone for road base, concrete aggregate, and as 'granite' for countertops, curbing, and monumental masonry.

Geological facts

Granodiorite is the rock that makes up the famous Rosetta Stone. It is chemically intermediate between granite and diorite, containing more plagioclase than orthoclase feldspar.

Field identification & locations

Identify in the field by its visible interlocking crystals and characteristic light gray color with dark flecks. It is commonly found in mountain ranges like the Sierra Nevada. Look for a rock that is harder than steel and has a speckled 'salt and pepper' appearance.

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