igneous

Diorite (River Pebble)

Phaneritic Intermediate Plutonic Rock (Diorite)

Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (black and white) appearance. Luster: Dull to sub-vitreous. Crystal Structure: Phaneritic (coarse-grained). Cleavage: Distinct in feldspar grains. Specific Gravity: 2.8-3.0.

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

Identified March 27, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of silicate magma below the Earth's surface (intrusive), typically at subduction zones. This specimen has been rounded and polished by fluvial (river) erosion.

Uses & applications

Used primarily as crushed stone for road construction and drainage. High-quality varieties are used as ornamental building stone ('black granite') or for floor tiles and graveyard markers.

Geological facts

Diorite was used in ancient Egypt for making hard stone sculptures, such as the famous statue of Khafre. The Code of Hammurabi was inscribed on an 8-foot tall diorite stele.

Field identification & locations

Identify in the field by the 'salt and pepper' look where the white (plagioclase feldspar) and black (biotite/amphibole) minerals are roughly equal. Found commonly in mountainous regions or riverbeds downstream from batholiths.

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)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral