igneous
Diabase (Dolerite)
Diabase
Hardness: 6-7 Mohs; Color: Dark grey to black with light plagioclase flecks; Luster: Sub-vitreous to dull; Crystal structure: Ophitic (fine to medium grained); Specific Gravity: 2.7-3.3
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black with light plagioclase flecks
- Luster
- Sub-vitreous to dull
Identified More igneous →
Explore Diabase (Dolerite) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black with light plagioclase flecks; Luster: Sub-vitreous to dull; Crystal structure: Ophitic (fine to medium grained); Specific Gravity: 2.7-3.3
Formation & geological history
Formed from the shallow cooling of mafic magma in dikes and sills. It is chemically equivalent to basalt but cools slightly slower, allowing for larger crystal growth.
Uses & applications
Used primarily as crushed stone for construction, road base, and railroad ballast. Exceptionally durable varieties are used for headstones and precision surface plates.
Geological facts
Stonehenge's inner circle 'bluestones' are made of a variety of diabase. It is often called 'Black Granite' in the commercial stone trade despite being a different rock type.
Field identification & locations
Look for a heavy, dark rock with a 'salt and pepper' appearance (white feldspar in dark pyroxene). Commonly found in rift zones or volcanic belts like the Palisades Sill in NY/NJ.
