igneous

Diabase (also known as Dolerite)

Diabase / Dolerite

Hardness: 6-7 (Mohs scale); Color: Dark grey to black, often with a greenish tint; Luster: Sub-metallic to dull; Crystal structure: Phaneritic/fine-grained crystalline; Cleavage: Generally poor; Specific Gravity: 2.7–3.3

Hardness: 6-7 (Mohs scale)
Color: Dark grey to black, often with a greenish tint
Luster: Sub-metallic to dull

Identified April 12, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the shallow intrusion of basaltic magma into dikes or sills. It cools faster than gabbro but slower than basalt, resulting in its characteristic medium-grained texture. Most common in tectonically active areas throughout Earth's history.

Uses & applications

Primarily used as crushed stone for construction (aggregate), railroad ballast, road base, and high-durability countertops. In ancient times, it was used for monuments (e.g., portions of Stonehenge).

Geological facts

Diabase is what makes up the famous 'Palisades' along the Hudson River in NY/NJ. Many 'bluestones' used at Stonehenge are actually of a similar dolerite composition.

Field identification & locations

Identify in the field by its dark color, crystalline texture (visible under a hand lens as interlocking 'salt and pepper' grains), and extreme hardness compared to sedimentary rocks. It often weathers to a rusty brown color on the surface due to iron content.

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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral