Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. The Mohs hardness is 6-6.5 and the specific gravity is 2.64-2.66. In color it is usually white, with shades of grey, green, or red.
Marcasite The mineral marcasite, sometimes called white iron pyrite, is iron sulfide (FeS2) with orthorhombic crystal structure. On fresh surfaces it is pale yellow to almost white and has a bright metallic luster. It tarnishes to a yellowish or brownish color and gives a black streak. It is a brittle material that cannot be scratched with a knife. It typically forms under low-temperature highly acidic conditions.