A black, mafic, fine-grained tabular intrusion between two layers of horizontal sedimentary rock must logically be a basaltic sil.
In geology, Basaltic sil is a dark colored igneous rock which is found between old sedimentary rocks.
Based on petrographic and chemical composition it has two types: alkali basalts and tholeiitic basalts.
This tubular intrusion type of sheet that is also found in volcanic lava, tuff and along foilation.
Generally this rock is formed as a result of lava flow therefore is named as extrusive rock.
Simply put, Basaltic sil is an intense colored igneous rock that is found among old sediments and metamorphic layers.
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