igneous

Diorite

Diorite (Intermediate intrusive igneous rock)

Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled black and white). Luster: Phaneritic (medium to coarse-grained crystals). Crystal Structure: Plagioclase feldspar, biotite, and hornblende. Cleavage: Good in two directions (feldspar). Specific gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: Salt and pepper (mottled black and white)
Luster: Phaneritic (medium to coarse-grained crystals)

Identified May 14, 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 at subduction zones. It represents an intermediate composition between granite and gabbro.

Uses & applications

Commonly used as a base material in construction of roads, buildings, and parking areas. It is also used as dimension stone for countertops, floor tiles, and grave markers, often sold as 'black granite'.

Geological facts

Diorite was used by ancient civilizations like the Egyptians and Sumerians for monumental sculpture because of its extreme hardness; the Code of Hammurabi was famously inscribed on a pillar of diorite.

Field identification & locations

Identify in the field by its characteristic 'salt and pepper' appearance and lack of visible quartz (unlike granite). Can be found in large batholiths in mountain ranges like the Andes or the Cascades.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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

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