Explanation

A class of igneous rocks with more than 90% of iron and magnesium minerals (mainly olivine and pyroxene). Most ultramafic rock are ultrabasic rocks, but they do not have the same relationship. ultrabasic rock are rock classified according to the standard of SiO2 content, while ultramafic iron rocks are determined according to the content of magnesium iron minerals. Such as pyroxenolite. Does iron and magnesium minerals contain more than 90%? However, the SiO2 content is higher than 45%, so it is ultramafic rock rather than ultrabasic rock; Another example is anorthosite, which is composed of calcium aluminosilicate minerals. SiO2 contains? F is lower than 45%, belonging to ultrabasic rock, but not ultramafic rock.

Classification