Geology Basics

How are igneous rocks formed

molten rocks deep in earth. intrusive form slowly beneath the earths surface. extrusive cool quickly above the earths surface. make up 65% of earths crust.

extrusive igneous rocks example:

basalt, obsidian, pumice

intrusive igneous rocks example:

granite, gabbro

how are metamorphic rocks formed

either igneous or sedimentary rocks come under intense pressure. changes the particle composition, creating new forms. old forms = parent rocks. 27% of earths crust. 

metamorphic rocks examples

slate, schist, marble, gneiss

how are sedimentary rocks formed

layers of material deposited into water bodies. build up, creating pressure, which compacts and cements, leading to crystals. 8% of earths crust.

sedimentary rocks example

limestone, chalk, sandstone, shale

lithology of a rock:

the physical and chemical composition of the rock itself.

structure of the rock:

the presence of joints, faults and bedding planes which are all cracks in the rock. It also includes whether there are pores within the rock that will tell you about its porosity and permeability.