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What is the composition of the Earth's mantle?

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The Earth's mantle is composed of rocks that have higher concentrations of mafic minerals (containing iron and magnesium) and lower in concentrations of the felsic minerals (aluminum and silica) than the rocks of Earth's crust.

The concentrations of the above elements therefore mean that the Earth's mantle is composed of a series of minerals that are predominately calcium / iron / magnesium aluminum silicates.

Such as:
  • Olivine - (Mg,Fe)2SiO4
  • Pyroxene - X(Si,Al)2O6, where X represents either calcium, sodium, iron or magnesium
  • Spinel - MgAl2O4
  • Garnet - X3Y2(SiO4)3 where X and Y can be a mixture of aluminum, iron, calcium, manganese or magnesium.



At depths shallower than approximately 460 km, these minerals form the rocks types Peridotite, Dunite (Olivine-rich Peridotite), and Eclogite.

At depths greater than 410 km Olivine becomes unstable and is replaced by a number of different mineral forms known as poly-morphs which are stable at higher pressures. These include Wadsleyite which forms at depths between 410 and 520 km and Ringwoodite which forms between 520 and 600 km deep.

These depths are based on a number of seismic discontinuities at the depths of 410 km (thought to mark the transition from Olivine to Wadsleyite) and at 520 km (thought to mark the transition from Wadsleyite to Ringwoodite) respectively.

At depths greater than around 650 km these upper mantle minerals start to become unstable due to the increased pressure and the minerals below this take the structure of the minerals Perovskite and Ferropericlase although with differing chemical compositions and it is this seismic discontinuity at 650 km depth that marks the transition to the lower mantle. The material at these depths is often referred to as the "post-perovskite" phase which is the high-pressure form of magnesium silicate (MgSiO3).


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What is the composition of the Earth's upper mantle?

The Earth's upper mantle is composed of rocks that have higher concentrations of mafic minerals (containing iron and magnesium) and lower in concentrations of the felsic miner
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What is the main composition of the mantle?

The answer that follows is good enough for personal knowledge or school students. Anyone higher than this should do read the Mantle page on wikipedia. Reference : NET The main