igneous

Granodiorite

Hardness: 6-7 on Mohs scale; Color: Salt-and-pepper (gray, white, black); Luster: Phaneritic (crystalline); Crystal structure: Coarse-grained intrusive; Cleavage: Specific to mineral components (feldspar/mica); Specific Gravity: 2.6-2.7

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

Identified May 30, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma beneath the Earth's surface. It is typical of continental crust and often found in mountain-building zones (batholiths). Most specimens range from Mesozoic to Cenozoic in age.

Uses & applications

Extensively used in construction as crushed stone or road base. Polished slabs are used for countertops, memorials, and architectural cladding. It is a major industrial aggregate.

Geological facts

Granodiorite is the intermediate rock between granite and diorite. One of the most famous historical uses of granodiorite is the Rosetta Stone, which was carved into a slab of this material.

Field identification & locations

Identify in the field by its coarse, speckled appearance and the presence of visible quartz alongside more plagioclase feldspar than orthoclase. Commonly found in large mountain ranges 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