igneous
Diabase (Wormstone or Pebble)
Diabase (Dolerite)
Hardness: 6-6.5 on the Mohs scale. Color: Brownish-grey to dark greenish-black with a speckled subophitic texture. Luster: Dull to earthy. Crystal Structure: Fine- to medium-grained, non-foliated. Cleavage: Poor/absent in hand specimen. Specific Gravity: 2.8 - 3.1.
- Hardness
- 6-6
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-6.5 on the Mohs scale. Color: Brownish-grey to dark greenish-black with a speckled subophitic texture. Luster: Dull to earthy. Crystal Structure: Fine- to medium-grained, non-foliated. Cleavage: Poor/absent in hand specimen. Specific Gravity: 2.8 - 3.1.
Formation & geological history
Formed by the relatively quick cooling of mafic magma injected into shallow crustal fractures (dikes or sills). The smooth, rounded pebble shape is the result of stream or coastal water erosion.
Uses & applications
Commonly used as crushed stone, construction aggregate, and dimension stone. Water-worn river pebbles are frequently used in landscaping, aquariums, or decorative rock collections.
Geological facts
Diabase shares the same chemical composition as basalt (extrusive) and gabbro (intrusive), but cools at an intermediate depth, giving it a distinctive interlocking micro-crystalline texture known as ophitic or subophitic texture.
Field identification & locations
Identified by its rounded cobble shape, heavy weight (high density), and characteristic speckled or interlocking crystalline texture visible under close inspection. Widely found in riverbeds, glacial deposits, and coastal beaches.
