There are three types of rocks: sedimentary, igneous, and metamorphic.
Sedimentary rocks are formed when sediment has been compacted (due to immense pressure) and cemented (a liquid has "glued" the sediments together). Some examples include sandstone, shale, gypsum, and limestone. There are two types of sedimentary rocks: Conglomerate and Breccia. An easy way to remember the difference between these two are the shapes of the sediments. Conglomerates have CIRCULAR deposits whereas Breccia has ANGULAR deposits (sharp angles).
There are two types of igneous rocks also: Intrusive and Extrusive.
Intrusive rocks have cooled slowly INSIDE the earth and usually have large crystals are visible to the naked eye. Examples: Granite, Gabbro, and Diorite.
Extrusive rocks have cooled very quickly as they EXITED the earth's crust. Examples: Basalt (ocean floor), Pumice (flying through the air from a volcano), Obsidian (black glass), and Rhyolite.
Metamorphic is the third type of rock. Any type of rocks can become metamorphic if it undergoes the right amount of heat and pressure. They are two types of metamorphic rocks: Foliated and Non- foliated.
- Foliated - has distinct lines in the rock. Examples: Granite -> Gneiss; Shale -> Slate
- Non-foliated - no visible layers. Examples: Quartz -> Quartzite; Sandstone -> Quartzite;
Limestone -> Marble.
Based on the rock cycle, any rock can turn into another type of rock given the correct situation.