1.- dunite and rock salt2.- peridotite and rock gypsum 3.- dolomite and obsidian4.- marble and schist
None of them are perfect. (1) Dunite is mostly olivine (90%), rock salt is halite.
I think 3 is probably closest, as dolomite can be exclusively calcium magnesium carbonate and obsidian is volcanic glass (silica). But obsidian is dark, typically black, because of many impurities, and strictly speaking obsidian is NOT a mineral because it is non-crystalline (as glass).
