Most are opaque due to their high content of iron or manganese. Many opaques are pedogenic minerals. They are also found as inclusions in other minerals. These minerals are usually studied in reflected light. Magnetite and Ilmenite are difficult to tell apart, both appear dull gray in reflected light.
Pyrite gives a pale brassy color with a metallic luster.
It often occurs as rectangular crystals. Pyrite is mainly associated with acid sulfate soils. Hematite has a metallic luster with a color ranging from dark steel gray, dull red, to iron black. Large crystals of hematite are a main constituent of most laterites. Goethite is one of the primary pigmenting agents in soils usually occurring as small grains dispersed throughout the matrix or as grain coatings.