igneous

Diorite

Phaneritic Intrusive Igneous Rock (Intermediate Composition)

Hardness: 6-7 Mohs; Color: Salt and pepper (dull white to grey and dark green to black); Luster: Subvitreous to dull; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions (due to amphibole/feldspar); Specific Gravity: 2.8-3.0.

Hardness: 6-7 Mohs
Color: Salt and pepper (dull white to grey and dark green to black)
Luster: Subvitreous to dull

Identified March 20, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of magma beneath the Earth's surface in volcanic arcs or mountain-building zones. This intermediate rock type forms between granitic and basaltic compositions and is typically associated with subduction zones.

Uses & applications

Used primarily in the construction industry as crushed stone for road bases and infrastructure. High-quality specimens are polished for use as 'black granite' countertops, floor tiles, and monumental masonry.

Geological facts

Diorite was used in ancient Egypt and Mesopotamia for sculptures and inscriptions because of its extreme hardness; the Code of Hammurabi was famously carved onto a diorite stele.

Field identification & locations

Identify in the field by its distinct speckling; it contains more dark minerals than granite but lacks the quartz content. Look for it in mountainous regions or exposed batholiths. Collectors should look for balanced 'dalmatian' patterns.

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