Rhyolite
Why is the rock called that and how is it formed?
Where did the name come from?
Rhyolite, a neologism composed of the Greek words ρέιν (rhein) = to flow and λιθος (lithos) = stone, is a volcanic rock. Baron Ferdinand von Richthofen described it scientifically for the first time in 1860.
How is rhyolite formed?
Rhyolite is formed where a magma chamber had formed in the upper crust of the Earth and did not erupt for thousands of years. During this long period of dormancy, most of the light elements — especially silicon oxide (SiO2) and most of the gases — accumulated in the conquered area of the chamber. In the process, rhyolite was formed in the uppermost areas of the magma chamber. Over a period of certainly 100,000 years, the SiO2 content increases from originally around 50% to as much as 78%. This is the essential difference between rhyolite and basalt.
If the magma then rises rapidly during a volcanic eruption, the remaining still liquid magma cools down very quickly and crystallises. This produces numerous, microscopically small crystals known as groundmass. The large crystals that are clearly visible to the naked eye are called ingots. They usually have a size between a few millimetres and several centimetres.
Where does the color come from?
After the eruption, aggressive volcanic gases flowed through the volcano, completely leaching out the originally rhyolitic rock and simultaneously depositing different minerals in it: Yellow, ochre and red are mostly the colours of iron minerals, the green shimmering sand-like material has been interspersed with very small celadonite crystals (called green earth in German).
Areas with large-scale rhyolite deposits in Iceland are Kerlingarfjöll and the popular Landmannlaugar, which lies further south. Both still have many fumaroles today, which are responsible for the leaching of the rock and make their landscape look so mystical.
Sources
- Islands Naturwunder
Christof Hug-Fleck
Edition World geographic
4. Edition 2010 - www.chemie.de
- Hálendið — Hochland
Das heiße Herz Islands
Christof Hug-Fleck within
Zauber des Nordens — das Nordmeer Magazin
Issue 2020.1 - www.steine-und-minerale.de