Mindat Description
fine-grained igneous rock that contains unusually high concentration of MgO
Geoscience Ontology Description
fine-grained igneous rock that contains unusually high concentration of MgO. For rocks that contain greater than 52 percent silica, MgO must be greater than 8 percent. For rocks containing less than 52 percent silica, MgO must be greater than 12 percent.