text: what is the most common mineral?   that would be quartz or sio2... aka silica or silicon dioxide.  there are many forms & colors of quartz such as clear, milky, rose, smokey, citrine, amethyst, etc. it is also found as opal which is non-crystalline silica (no crystals).  it is found as sand grains, as quartz veins, & in rocks such as granite. it is also found alone such as above. sio2 is also part of a major mineral group called the silicates.  feldspar is also common but it is one of the most common rock-forming minerals. feldspar easily weathers & is broken down into clay in warmer wetter climates (ie southern states & the tropics)