igneous

Diorite (Polished River Pebble)

Diorite (Intermediate intrusive igneous rock)

Hardness: 6-7 Mohs; Color: Salt-and-pepper (white plagioclase with black hornblende/biotite); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0

Hardness: 6-7 Mohs
Luster: Dull to sub-vitreous

Identified April 8, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: Salt-and-pepper (white plagioclase with black hornblende/biotite); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0

Formation & geological history

Formed from the slow cooling of magma beneath the Earth's surface (intrusive) in volcanic arcs and mountain-building zones. This specific specimen has been rounded and smoothed by water erosion/alluvial processes.

Uses & applications

Used in construction as crushed stone, for floor tiles, countertop surfaces (often sold as 'black granite'), and as decorative landscaping stones.

Geological facts

Diorite was used in ancient Egypt and Mesopotamia for sculptures and stelae because of its extreme hardness; the famous Code of Hammurabi was inscribed on a diorite pillar.

Field identification & locations

Identified by its phaneritic texture with a balanced mix of light and dark minerals. Commonly found in roots of mountain ranges or as eroded pebbles in riverbeds and beaches.

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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)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral