igneous

Diorite (River Pebble)

Diorite (Intermediate intrusive igneous rock)

Hardness: 6-7 on Mohs scale; Color: Black and white (salt and pepper appearance); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: Black and white (salt and pepper appearance)
Luster: Dull to sub-vitreous

Identified May 16, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Black and white (salt and pepper appearance); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0.

Formation & geological history

Formed through the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones. This particular specimen is a water-worn river pebble, likely rounded by alluvial transport during the Quaternary period.

Uses & applications

Used as crushed stone for road construction, drainage, and concrete aggregate. Polished pieces are used for cemetery monuments, floor tiles, and decorative architectural stone.

Geological facts

Diorite is often called 'salt and pepper rock' due to the contrasting light plagioclase feldspar and dark hornblende/biotite minerals. It was famously used in Ancient Egypt for sculptures, including the Code of Hammurabi stele.

Field identification & locations

Identify by its phaneritic texture and lack of visible quartz (distinguishing it from granite). It is commonly found in mountainous regions near continental margins. Collectors look for high contrast and smooth rounding in stream beds.

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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

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

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Magnetite

Magnetite (Fe3O4)

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