What can cause rock?

Answer 1

Rocks come in two basic types - igneous and sedimentary.

Igneous rock is formed from liquid rock in the form of magma or lava that cools and can vary widely in characteristics depending on how it cools - and how quickly, as well as the chemical content of the material that it formed from.

The second main type is rock that is formed of sediments, such as a silt or organic matter that settles in layers in lake/sea beds or is otherwise deposited and with time and pressure becomes solid and forms rock - often rock with definite layers such as common shale, or more homogenous rock like sandstone where the strata (layers) may not be so easily seen.

There is a third classification, metamorphic rock (metamorphic meaning change in form) that is really only one of the first two, that has been altered through time, heat, pressure or exposure to other chemical factors that have altered the original rock significantly enough that it is considered another type of rock entirely with different characteristics from the original rock, such as grain size, density, etc.