Sedimentary Rock

This type of rock is significantly different to that of igneous rock. This is because sedimentary rock is made out of other rock materials or the sediments of plantlife and marine organisms compressed. Sedimentary rock is formed through pressure underwater causing the sediments to turn solid. They are laid out into various layers called strata. There are three types; organic, inorganic and chemically derived. An example of an organic sedimentary rock is limestone. It is mostly made out of the fossils of organisms compressed. Another example is peat. An example of an inorganic sedimentary rock is sandstone and is made out of compressed rock materials and does not contain any organisms. An example of a chemically derived rock is gypsum and can be found in Cavan, but the most valueable example would be oil and gas such as that found off the coasts of Ireland.

Limestone is commonly found in the central plains of Ireland. Limestone rock would be used for construction as it is a very hard rock. The most noted limestone landscape in Ireland is in The Burren Co. Clare. This is due to the interesting features created by the erosion of the limestone by rain. This is called a Karst landscape and occurs when carbon dioxide in the rain creates a weak carbonic acid which erodes at calcium carbonate in the limestone to make a solution. This solution contains calcite and as water runs in streams through the limestone pavement it deposits this calcite. Over long periods of time this calcite deposit builds into features such as stalactites and stalagmites that are found in the caverns eroded through this process.

Formula for carbonic weathering - H2CO3 + CaCO3 → Ca(HCO3)2

Sandstone is the second most common rock found in Ireland and can be found in the Magillicuddy Reeks Co. Kerry. It can also be used as a building material depending as some is soft and some is hard. It is usually permeable but this depends on the rate of compression of the sand grains in the rock. It is formed in two stages, sedimentation and cementation. A layer of sand accumulates as a result of sedimentation. This layer can form from the suspension layer in water settling to the bottom. or from sand in the air in a desert. After this first layer accumulates it is compressed by overlying layers and cemented by materials such as silica and calcium carbonate. The color of sandstone can alter depending on the area and individual materials found in it. Usually it is yellow/brown but in parts of America where iron oxide (rust) is a component in is a brick red. Similarly if manganese is a component in can have a purple hue.

This is a photo of the karst landscape in The Burren and the clints and grikes created through this chemical process.