Rock Types - Igneous Rock
- Formed from cooled, solid molten rock.
- Rocks melt when pushed down due to high pressure.
- When cooled forms many crystals due to all the minerals in the rock:
- if cooled fast e.g in water the crystals are small and are called extrusive igneous rock
- if cooled slowly e.g inside the earth in cracks the crystals are big this is called intrusive ingneous rock.
- Examples include Basalt and Granite.
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Rock Types - Sedimentary Rock
- Formed by the laying down of rock particals - sediment, also known as deposition.
- The sediment comes from eroded rocks carried there by rivers or ice, and from the skeletons of sea creatures.
- They are found on the surface of the earth.
- Loose and crumbly.
- Fossils are found in the rock.
- Examples include Limestone, Chalk.
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Rock Types - Metamorphic Rock
- Formed under the earth under imense pressure and heat, within the earths crust altering the structure and composition of the rock.
- Dense compact rocks usually making them resistant to weathering and erosion.
- The rock is a mix of sedimentary and ingneous rock,
- Exmaples include slate and marble.
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Rock Types - Key words
- Crystallisation - the formation of crystals.
- Extrusive - A rock forced out of the earths surface.
- Intrusive - A rock that is forced into the cracks of other rocks and forms under the surface.
- Lithification - Process in which loose materials are converted into solid rocks.
- Erosion - The wearing away of the land.
- Weathering - Breakdown of rocks by the action of rain, snow and cold.
- Geologist - Classifies rocks into 3 different types.
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Limestone - What is Limestone
- Limestone is a organis, sedimentary rock.
- It is made up of tiny shells and micro-skeletons from the seabed
- It is compressed and layered this is called bedding planes
- There are vertival cracks these are called joints, this makes it permable
- The rock is made up of calcium carbonate ( which reacts with dilute hydrolic acid (acid rain)).
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Limestone - How is it formed
- Britain once had a tropical climate where most of england and wales was covered by warm tropical sea, This period of time was called the carboniferous era about 350 milliom years ago. Over time the seas dried put leaving behind a host of shelly creatures that became buried in mud and became squashed. Over time, pressure and heat cemented together the sediment. Due to continuous deposition formed horizontal layers called bedding planes. Fossils tell us what lived at the same time the rock was made. Finally due to tectonic movement, carboniferous limestone was squeezed up above sea level and can be found in many locations in britain today!
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- Caverns - underground that have been hollowed out by the action of underground streams and by crabonation and soultion
- Swallow/Sink holes - where rivers flow down into the rocks, swallow holes are larger than sink holes. They are formed by constant chemical attack and also the collapse of a cavern.
- Pillars - where stalactite and a stalagmite have joined.
- Limestone pavement - is larged expossed limestone that is constantly been eroided and weathered, grikes are the large cracks and clints is the stone. When the overlying rock was eroide the pressure realese caused the stone below to crack.
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Limestone Features continued
- Resurgance point - where streams underground re-emerge at the surface, usally happens where the stream reaches inpermeable rock
- Underground stream - flows down through the limestone carving out caverns until it reaches a layer of impermeable rock below the limestone layer.
- stalagmites and stalactites - left over minerals from the evaporated water drips from the roof of the carvern, stalacties are on top and stalagmites on the bottem.
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