BIR-1a-NP

Mafic rocks are characterised by a silica content of 45-52 m/m% and similar to ultramafic rocks also consist mainly of olivine and pyroxenes. They do however often also contain the calcium-rich varieties of feldspar and can contain iron-rich micas such as biotite. Basalts make up the oceanic crust, but can also be found on continents as so called Large Igneous Provinces (LIPs).