Why are there 3 categories of rocks?

Types of Rocks. Rocks are not all the same! The three main types, or classes, of rock are sedimentary, metamorphic, and igneous and the differences among them have to do with how they are formed. Sedimentary Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. read more

Types of Rocks Rocks are not all the same! The three main types, or classes, of rock are sedimentary, metamorphic, and igneous and the differences among them have to do with how they are formed. Sedimentary Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. read more

The types and abundance of minerals in a rock are determined by the manner in which it was formed. Many rocks contain silica (SiO 2); a compound of silicon and oxygen that forms 74.3% of the Earth's crust. read more