About half of all minerals are silicates. Magma is around 50% to 60% silica. The other common elements -- aluminum, iron, magnesium,and the alkaloids (calcium, sodium ande potassium) - make up most of the balance. The rest of the near-100 elements are found in magmas only as traces. Silica combines with many other elements to make the rock-forming minerals such as feldspar. Any excess then separates as quartz, in a host of sizes, shapes and forms.