igneous

Diabase (also known as Dolerite)

Diabase

Hardness: 6-7 on Mohs scale; Color: dark grey to black with light brown weathering; Luster: dull to sub-metallic; Crystal structure: fine to medium grained ophitic texture; Cleavage: poor; Specific gravity: 2.7-3.3

Hardness: 6-7 on Mohs scale
Color: dark grey to black with light brown weathering
Luster: dull to sub-metallic

Identified May 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the shallow-level cooling of mafic magma, often occurring in sills or dikes. This specimen shows significant rounding due to fluvial (river) or glacial transport.

Uses & applications

Used primarily as crushed stone for construction, road aggregate, and railroad ballast monument stone (black granite trade name).

Geological facts

Highly durable and dense, diabase makes up the famous Palisades Sill along the Hudson River. It is chemically similar to basalt but has a coarser grain size due to slower cooling underground.

Field identification & locations

Identify in the field by its high density, dark interior color, and typical brown weathered 'rind'. Found globally in areas of volcanic activity or ancient rifting.

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