First, we’ll make sure we know what these terms mean.
Igneous and metamorphic rocks: igneous – rocks that have formed from the cooling of magma. Metamorphic rocks are rocks that have been altered. Amphibole etc. These are types of minerals that are part of the recipe of igneous rocks. Plutonic: cooled beneath the earth surface
Felsic: more feldspar mineral and more silica
Mafic – more magnesium and iron rich minerals.
Peridotite – the rock that forms in the mantle – lots of minerals olivine and pyroxene.
Mafic – so magnesium and iron rich (ferric) minerals that we’ll look at in labs Gabbro and basalt are both formed from the cooling of magma – but they differentiate because of different rates of cooling. Last week we had a quick introduction to plate tectonics and diverging oceanic plate boundaries where magma rises – this image represents the composition of those regions.
This sample of peridotite is sitting inside some basalt. This makes the peridotite a xenolith. Think of xenophobia – a fear of outsiders or strangers – in the case of the xenolith – it’s a foreign body of rock hosted inside another rock type. So our peridotite hitched a ride up through the mantle on board some rock that cooled around the peridotite. Sometimes peridotite can bring up diamonds with it – and in that case the diamond is the xenolith. It’s very rare – hence why diamonds are so expensive The material on the right, the gneiss – looks quite different to the peridotite. That would suggest that we may have different minerals – and different minerals mean different environment and or/different processes. The gneiss is a metamorphosed rock – so a rock that has been transformed from its original form due to heat and or pressure. Gneiss makes up most of earths lower crust – the pressure and heat transforms sedimentary and igneous rocks.
The size of Earth has been deduced as far back as the fifth century B.C.E. Earth’s mass is derived...
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