igneous
Dark coarse-grained igneous rock, likely gabbro or diabase
Gabbro–diabase; chiefly plagioclase feldspar and pyroxene, with possible olivine and opaque iron-titanium oxides
AI-generated identification · may be incorrectTypically dark gray to black, granular, and speckled with a subvitreous to dull luster; hardness about 6–7, no obvious cleavage at specimen scale, and specific gravity roughly 2.8–3.1. The image is cropped and texture-based identification is uncertain.
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Physical properties
Typically dark gray to black, granular, and speckled with a subvitreous to dull luster; hardness about 6–7, no obvious cleavage at specimen scale, and specific gravity roughly 2.8–3.1. The image is cropped and texture-based identification is uncertain.
Formation & geological history
Forms when mafic magma cools slowly underground (gabbro) or in shallow dikes and sills (diabase/dolerite), producing interlocking crystals. Most examples range from Precambrian to Mesozoic or younger, depending on the locality.
Uses & applications
Used as crushed aggregate, roadstone, riprap, dimension stone, countertops, monuments, and occasionally decorative polished stone; generally low gem or collector value.
Geological facts
Its dark color reflects abundant iron- and magnesium-rich minerals, while pale flecks are commonly plagioclase. Diabase dikes can form extensive, resistant ridges and are important markers of ancient tectonic and volcanic activity.
Field identification & locations
Look for a dense, hard, dark rock with visible interlocking white-gray feldspar and black pyroxene grains; it is not strongly layered or glassy. Common worldwide in mafic intrusions and oceanic crust; a fresh surface and hand lens help distinguish it from basalt.
