The most abundant mineral in a sandstone is usually quartz, because it is the hardest one of the rock forming minerals and therefore the most resistant to abrasion during transport. The second most abundant mineral is feldspar (potassium feldspar), followed by micas. These minerals are also the chemically most stable (under conditions of the Earth's surface) among the rock forming minerals. The softer and less stable minerals (hornblende, pyroxene, olivine) are absent or at least fairly rare. Even though the mineral composition of a sandstone does not give us lots of direct clues as to the source rock composition,