igneous

Diorite

Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (black and white/mottled gray); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Composition: Mostly Plagioclase feldspar and Hornblende/Biotite.

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

Identified April 8, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of magma (intrusive) within the Earth's crust, typically in volcanic arcs and above subduction zones at convergent plate boundaries.

Uses & applications

Used primarily in construction for crushed stone, road base, and as dimension stone for buildings, countertops, and floor tiles. Occasionally used as a base for carvings.

Geological facts

Diorite is often mistaken for granite, but it has little to no quartz. Historically, it was used by ancient civilizations like the Egyptians and Sumerians for sculptures and stelae (such as the Code of Hammurabi) because of its extreme hardness.

Field identification & locations

Identify in the field by its distinctive black and white speckled appearance with visible interlocking crystals and an absence of pinkish potassium feldspar. Commonly found in roots of mountain ranges.

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