olivine

This term refers specifically to a group of magnesium-iron silicate minerals. It is characterized by a distinct olive-green hue, which gives the mineral its name and serves as a primary diagnostic feature for geologists identifying mantle-derived rocks.

As a mass noun representing a mineral species, it is treated as uncountable in scientific contexts. One does not typically refer to multiple olivines unless discussing different chemical varieties or specific crystal grains, in which case a partitive like crystals of olivine or grains of olivine is used.