igneous
Olivine Diabase (Microgabbro)
Diabase or Dolerite with Olivine
Hardness: 6-7 Mohs; Color: Dark grey to greenish-black with light green phenocrysts; Luster: Sub-vitreous to dull; Crystal structure: Fine-grained with intergranular textures; Specific Gravity: 2.7-3.3
- Hardness
- 6-7 Mohs
- Color
- Dark grey to greenish-black with light green phenocrysts
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to greenish-black with light green phenocrysts; Luster: Sub-vitreous to dull; Crystal structure: Fine-grained with intergranular textures; Specific Gravity: 2.7-3.3
Formation & geological history
Formed through the cooling of mafic magma within shallow dikes or sills (intrusive). The presencia of small green olivine crystals suggests a mantle-derived magma source cooling relatively quickly near the surface.
Uses & applications
Used primarily as crushed stone for road construction, railroad ballast, and higher-quality building stone (black granite).
Geological facts
Diabase is the primary rock type of the Famous Palisades Sill along the Hudson River. Its fine-grained structure makes it exceptionally durable and resistant to compression.
Field identification & locations
Identify in the field by its high density, dark color, and characteristic 'salt and pepper' appearance with subtle green specks. Found commonly in areas of crustal thinning or rift zones.
