igneous

Diabase (Greenstone)

Diabase (Dolerite)

Hardness: 6-7 Mohs; Color: Dark green to black with mottled light green/grey spots; Luster: Dull to sub-vitreous; Structure: Fine-to-medium grained phaneritic (crystalline); Cleavage: Indistinct; Specific Gravity: 2.7-3.3.

Hardness: 6-7 Mohs
Color: Dark green to black with mottled light green/grey spots
Luster: Dull to sub-vitreous

Identified March 16, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of mafic magma (basaltic composition) in shallow intrusive bodies like sills, dikes, or plutons. Commonly associated with the Mesozoic era in North America during the breakup of Pangaea.

Uses & applications

Extensively used as 'crushed stone' for road construction, railroad ballast, and high-strength concrete. Higher quality slabs are used for countertops, monuments, and as ornamental 'black granite'.

Geological facts

Many of the stone circles at Stonehenge were made from 'bluestone,' which is a variety of dolerite/diabase. In the US, the Palisades Sill along the Hudson River is one of the most famous diabase formations.

Field identification & locations

Identify in the field by its high density, dark greenish-grey weathered surface, and interlocking crystalline texture that looks like 'salt and pepper' up close. Found globally, especially in rift basins like the Appalachian range or Western Australia.

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