igneous

Granodiorite Pebble

Granodiorite

Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled gray, white, and black). Luster: Dull to phaneritic. Crystal structure: Medium to coarse-grained phaneritic texture. Cleavage: Distinct in feldspar grains.

Hardness: 6-7 on Mohs scale
Color: Salt and pepper (mottled gray, white, and black)
Luster: Dull to phaneritic

Identified May 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of silica-rich magma beneath the Earth's surface (intrusive). This specimen has been rounded and smoothed by water erosion, likely in a riverbed or coastal environment.

Uses & applications

In crushed form, it is used for road base and concrete aggregate. Large deposits are quarried for dimension stone and architectural cladding.

Geological facts

Granodiorite is intermediate between granite and diorite. The famous Rosetta Stone was carved from a slab of granodiorite.

Field identification & locations

Identify by its 'salt and pepper' appearance and visible interlocking crystals. It is richer in plagioclase feldspar than orthoclase. Commonly found in batholiths and mountain ranges like the Sierra Nevada.

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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