Diabase
“The hard rock of ancient sills and dykes”
Diabase (or dolerite) is a medium-grained mafic intrusive rock with the same composition as basalt and gabbro but a texture in between. It typically forms in shallow sills and dykes and is prized as one of the toughest construction aggregates and dimension stones available.
plagioclase feldspar, augite, olivine (minor), magnetite, ilmenite
Palisades Sill (New Jersey, USA), Karoo Basin (South Africa), Tasmania (Australia), Whin Sill (England), Deccan (India)
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The dramatic Palisades cliffs along the Hudson River across from Manhattan are a massive diabase sill that intruded about 200 million years ago as the Atlantic Ocean first began to open.
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Where in the oceanic crust does diabase typically form?
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