Crustal plates form the outer layer of the Earth. There are seven major plates and many smaller plates. These tectonic plates are formed from the Earth's crust and uppermost part of the mantle.Types of tectonic plates. There are two types of tectonic plates.Continental plates are made primarily of granitic rocks and are much thicker and older.ntroduction. Crustal plates form the outer layer of the Earth. There are seven major plates and many smaller plates. These tectonic plates are formed from the Earth's crust and uppermost part of the mantle. Types of tectonic plates. There are two types of tectonic plates.