Rocks at Cliffe Castle Museum
Types of Rock
What is a rock?
A rock is basically a mixture of different minerals bonded together in a lump. Rocks are commonly defined and grouped by how they are formed.
Igneous rocks are like the angriest person in the classroom, hot-headed, potentially violent but eventually they cool down.
When very hot liquid rock (magma) cools slowly inside Earth, or when it cools more rapidly after reaching the surface, igneous rocks are formed. Igneous rocks are the rocks of explosive volcanoes and destructive pyroclastic flows (mixtures of hot gas, ash and other volcanic rocks travelling very quickly down the slopes of volcanoes).
Examples of igneous rocks are granite, lava, obsidian, pumice and basalt.
Every minute of every hour of every day, particles of gravel, sand, mud, silt, even dead animals and plants are being transported into bodies of water and deposited there. They are the mud at the bottom of a lake and the sand under the sea.
Eventually, and we’re talking many thousands of years, this ‘sediment’ becomes compacted and cemented together forming sedimentary rock. Fossils are found in sedimentary rock. Examples of sedimentary rocks are sandstone, limestone, flint, mudstone (shale), clay, conglomerate, breccia and gypsum.
Take any rock type, give it to Mother Earth and get her to knead it and bake it. Have a little patience and out of her oven will come a metamorphic rock.
Metamorphic rocks are formed when the vast amounts of pressure and heat found inside Earth change a rock physically and or chemically. The original rocks can be igneous, sedimentary or metamorphic yet the outcome of their change is always a very different metamorphic rock. Examples of metamorphic rocks are marble, slate and schists.