igneous
Diabase (Dolerite)
Mafic Intrusive Igneous Rock
Hardness 6-7, color dark grey to black with salt-and-pepper texture, dull to sub-metallic luster, fine-to-medium grained crystalline structure, specific gravity 2.7-3.3
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Physical properties
Hardness 6-7, color dark grey to black with salt-and-pepper texture, dull to sub-metallic luster, fine-to-medium grained crystalline structure, specific gravity 2.7-3.3
Formation & geological history
Formed from the rapid cooling of basaltic magma within shallow crustal intrusions such as sills and dikes.
Uses & applications
Crushed stone for road beds, railroad ballast, building foundations, and sometimes used as dimension stone for monuments.
Geological facts
Diabase is chemically identical to basalt but has a larger grain size due to cooling underground rather than on the surface.
Field identification & locations
Identify by its interlocking crystal 'ophitic' texture under a lens and its high density; commonly found in rift basins and volcanic regions.
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Blue Apatite
Fluorapatite (Ca5(PO4)3F)
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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
Magnetite
Iron(II,III) oxide (Fe3O4)
mineral
Blue Apatite
Apatite (Group), Ca5(PO4)3(F,Cl,OH)
mineral
Sodalite
Sodalite - Na8(Al6Si6O24)Cl2
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Magnetite
Magnetite (Fe3O4)
mineral