igneous

Diabase (Greenstone)

Diabase (also known as Dolerite)

Hardness: 6-7 on Mohs scale; Color: Dark grey to greenish-black; Luster: Sub-vitreous to dull; Crystal structure: Fine to medium-grained phaneritic (ophitic texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.7–3.3.

Hardness: 6-7 on Mohs scale
Color: Dark grey to greenish-black
Luster: Sub-vitreous to dull

Identified March 28, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the shallow cooling of mafic magma in intrusive bodies like sills and dikes. Historically associated with the Triassic-Jurassic period (approx. 200 million years ago) in areas like the Central Atlantic Magmatic Province.

Uses & applications

Used primarily as crushed stone for construction (road base, railroad ballast) and 'black granite' for monuments. Some varieties are polished for ornamental use.

Geological facts

Stonehenge's inner 'bluestones' are made of a type of diabase. It is chemically equivalent to basalt but has larger crystals due to slower cooling underground.

Field identification & locations

Identify in the field by its distinctive 'salt and pepper' appearance under a hand lens and its heavy weight for its size. Common in the Appalachian mountains (USA), UK, and South Africa. Collectors should look for weathered surfaces which often turn brown.

Other igneous specimens

See all

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