Rock formations

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Igneous processes

rocks or processes involving molten rock

igneous extrusion: friction, heat and pressure, cause molten rock (magma) to be forced upwards to the surface, when it reaches the surface it can cool rapidly and form fine-grained rock e.g Basalts

Batholiths: Some magma my fail to reach the surface, forming a large molten mass of intrusive rock. This insulates the surrounding rock so it cools slowly, which produces large crystals and gives more time of minerals to be separated into localised concentrations. Graphite is produced in these deep batholiths

Hydrothermal deposits: Cracks may form around the batholith, allowing hot solution containing dissolved minerals to escape to the surface. As the solutions cool they deposit minerals in a predictable order in relation to their solubility. This process takes mixed mineral solutions and separates them into localised concentrations that are easier to exploit. Most metals e.g iron, tin, copper, and lead are found as hydrothermal deposits

Sedimentary processes

material or process involving materials being carried by water or air and then being deposited

alluvial/placer deposits: carried by flowing water but are deposited when the water slows down. Different minerals are deposited at different parts of the river, the densest first. Tin ore, gravel, sand and clay are deposited int this way.

Evaporites: when water evaporates from mineral rich solutions. Minerals crystallise as the solution becomes more saturated, each mineral crystallises at different times so they form layers. E.g Gypsum is deposited before halite

Biological deposits: processed from dead animals and plants. Fossil fuels are produced by dead organisms partially decaying in anaerobic conditions. Chalk and limestone are formed from the shells of dead marine organisms.

Metamorphic processes

existing rock is exposed to extreme heat and pressure from nearby igneous activity, causing the rock to change form without it fully melting. Slate is formed from sedimentary shale, made largely form clay.