Rhyolite

See also: Rhyolite (homonymy)

The rhyolite is a explosive Roche volcanic vitreous made up of Quartz, of Feldspaths, Amphibole. It is a rock with the microlithic structure being able all the same to present minerals visible with the eye naked.

The rhyolite is classified in the extrusives rocks known as igneous. Its density is from 2.3 to 2.6 g/cm ³. The rhyolite is the volcanic equivalent of the Granite.

A rhyolite comes from refroisissement from a magma of rhyolitic composition, rich in Silice SiO2, like the granite.

The rhyolite term comes from the Greek rheîn , to run, and lithographies , stone. That comes from the fluidal structure of the rock, whose orientation of the Microlite S shows the flow in the liquid in cooling. That is surely with the rhyolitic Viscosité important of the magma.

Layers

Currently, the eruptions of rhyolitic lava are rare, apart from some areas like the Iceland.

In France, in the department of the VAr, it is the rhyolite amaranth which contributes to the beauty of the landscapes of the Massif of Esterel, volcanic solid mass of age Permien.

The rhyolite can be also found close to zones of Geyser S.

Use

For these properties the rhyolite is used like Ballast railways and in particular those of TGV.

Rhyolitic origin of the magma

The Magma at the origin of the rhyolites is formed:
  • either starting from a fusion partial of the continental Earth's crust (Carboniferous case of the rhyolites of Montreuillon in the Morvan),
  • or generally, by differentiation of a basaltic magma (tholeitic especially), thus coming from fusion partial of the Peridotite of the coat, as it is the case for the rhyolites of Iceland.

The crustal or mantellic origin perhaps determined by the isotopic report/ratio of the Strontium:

  • the rhyolites of mantellic origin have a 87Sr ratio/86Sr of about 0,702.
  • the rhyolites of crustal origin have a higher 87Sr ratio/86Sr, until 0,710.

References

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