Dacite

Dacite (/ˈdeɪsaɪt/) is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides.

The word dacite comes from Dacia, a province of the Roman Empire which lay between the Danube River and Carpathian Mountains (now modern Romania and Moldova) where the rock was first described.

[1] The term dacite was used for the first time in the scientific literature in the book Geologie Siebenbürgens (The Geology of Transylvania) by Austrian geologists Franz Ritter von Hauer and Guido Stache.

Sanidine occurs, although in small proportions, in some dacites, and when abundant gives rise to rocks that form transitions to the rhyolites.

The groundmass of these rocks is often aphanitic microcrystalline, with a web of minute feldspars mixed with interstitial grains of quartz or tridymite; but in many dacites it is largely vitreous, while in others it is felsitic or cryptocrystalline.

When this slab reaches the mantle and initiates the dehydration reactions, minerals such as talc, serpentine, mica and amphiboles break down generating a more sodic melt.

Today, the colder oceanic crust that subducts under most plates is not able to melt prior to the dehydration reactions, thus inhibiting the process.

[1] Other occurrences of dacite in Europe are Germany (Weiselberg), Greece (Nisyros and Thera), Italy (in Bozen quartz porphyry, and Sardinia), Austria (Styrian Volcano Arc), Scotland (Argyll),[20] Slovakia, Spain (El Hoyazo near Almería),[21] France (Massif de l'Esterel)[22] and Hungary (Csódi Hill).

[23] Sites outside Europe include Iran, Morocco, New Zealand (volcanic region of Taupo), Turkey, USA and Zambia.

[citation needed] Dacite is found extraterrestrially at Nili Patera caldera of Syrtis Major Planum on Mars.