Fundamentals Of Geology Title

Of course the most important thing about geology is the world itself. The center of the Earth is a molten, super-hot core, made up of the inner and outer core. The core is 2,440km in diameter. Less heavy rock surrounds this core and is called the mantle, this mantle is semi-fluid due to the temperatures and pressures of the core. Floating upon the mantle is lighter still rock, called the crust. Six to thirty kilometers thick, it is deepest under the continents and shallower under the oceans. More than 90 elements occur within the Earth, whilst just eight form almost all the crust. Seventy-five percent of the crust is indeed oxygen and silicon.

Rocks are formed in one of three ways. Igneous rocks are those that cool down from volcanic activity, thrown out by volcanoes or lava flows that cool under the earth. Animal or plant remains also build up and igneous rock becomes weathered; these remains or exposed rocks are then worn down by the weathering action of rain, temperature and wind, and small particles are washed down by rain and rivers to lower levels where they settle and the sediment becomes crushed and layered into sedimentary rocks. Both igneous and sedimentary rock is placed under great pressure by heat from below, the movement of the plates or other means that cause their chemical structure to change and these 'altered rocks', then formed, are called metamorphic.

Mineral streak - the colour of which can help identify it. This pyrite leaves a black streak.The rock is composed of different minerals. The constituent minerals determines the type of rock and each mineral has its own crystalline structure. Each kind of mineral is unique to its type. To define a particular mineral it needs to be tested using some very basic techniques and methods. Of course the chemical formula for each mineral can be found by geologists or chemists using high-tech equipment and methods, but to the simple geologist (professional or amateur) the best practices to determine a particular mineral is to discover their crystal form, hardness, streak and cleavage. Other means include atomic weight.

Most minerals have crystal forms that are fairly unique to that mineral, but overcrowded crystals can be deformed and grow irregularly. Hardness is a comparative guide of one mineral to another. Friedrich Mohs, an Austrian, in 1822 devised the Moh's Scale of Hardness. This rated ten minerals by their hardness and all other minerals can be classed by their hardness comparatively. The scale runs from 1 (the softest - talc), to 10 (the hardest - diamond). Diamond is four million times harder than talc. Colour varies depending upon impurities that may be present in some forms of mineral, however, their true streak may be discovered by scratching it upon a white substance harder than itself. Glassy, greasy or metallic lustre exists and each mineral has its own specific colour. Cleavage is the plane of fracture that occurs when the crystal is broken. some shatter into different planes while some only break along certain directions.

The Core

The Crust

 

 

 

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Last Updated: 29th February 2004