igneous

Diorite

Phaneritic plutonic rock (dominated by plagioclase feldspar and hornblende)

Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (black and white/gray); Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions (feldspar); Specific gravity: 2.8-3.0.

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

Identified March 21, 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 (subduction zones). It typically dates from the Proterozoic to the Cenozoic eras.

Uses & applications

Used primarily as structural stone, crushed stone for road base, and decorative architectural stone (granite-like countertops or floor tiles). Historically used by ancient Egyptians and Mayans for sculpture.

Geological facts

Diorite was used to carve the famous Code of Hammurabi, one of the oldest deciphered writings of significant length in the world, due to its extreme durability and toughness.

Field identification & locations

Identify by its coarse-grained texture where dark minerals (hornblende/biotite) and light minerals (plagioclase) are roughly equal in abundance. Found in mountainous roots like the Andes or the Alps. For collectors: look for 'orbicular' varieties which are highly prized.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral