igneous

Diorite (River Rock)

Intermediate plutonic igneous rock

Hardness: 6-7 on Mohs scale. Color: 'Salt and pepper' (gray/white and black/dark green). Luster: Dull to sub-vitreous. Structure: Phaneritic (coarse-grained). Cleavage: Two directions (mostly from amphibole/feldspar). Specific gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: 'Salt and pepper' (gray/white and black/dark green)
Luster: Dull to sub-vitreous

Identified April 10, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones. This particular specimen is water-worn, smoothed into a cobble by river or glacial erosion over thousands of years.

Uses & applications

Used as crushed stone for road construction and drainage. High-quality diorite is sometimes polished as 'black granite' for countertops or cemetery monuments. Occasionally used for carvings.

Geological facts

Diorite was used by ancient civilizations for sculpture and tools due to its extreme hardness; the famous Code of Hammurabi was inscribed on a massive diorite stele.

Field identification & locations

Identify in the field by its speckled 'salt and pepper' appearance and large visible mineral crystals. Unlike granite, it lacks significant quartz. Commonly found in areas with tectonic or volcanic history.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral