Over 2000 minerals have been found to this day. The minerals are put into two groups due to their chemistry. Silicate minerals are the most common mineral groups that form when molten rock cools either at or near the earths surface or deep underground. Non-silicate minerals form when magma cools, while others form when water evaporates away leaving crystals behind, or when other minerals decompose. Feldspar is the most common mineral in the earth's crust.