What is a tranchyandesite in geology ?
Trachyandesite : definition
A trachyandesite is a volcanic rock of gray tint, fluidal microlithic, sometimes porphyritic. It is composed of plagioclase (oligoclase, andesine), alkaline feldspar (orthoclase, sanidine), with, depending on the variety, biotite, augite, hypersthene, hornblende, quartz or olivine.
The mineralogical particularities, in particular the nature and the proportions of feldspars and ferromagnesians, define the varieties. Latite is considered a variety of trachyandesite containing as much sanidine as plagioclase.
Trachyandesites are lava forming thick flows and peaks, very common in Auvergne. Volvic stone is a trachyandesite produce by the Puy de la Nugère which has been used extensively in construction (Clermont-Ferrand cathedral) and as a support for enamelling, while sancyite is a trachyandesite with sanidine phenocrysts that found it on the crests of Puy de Sancy (Mont Dore).
The mineralogical particularities, in particular the nature and the proportions of feldspars and ferromagnesians, define the varieties. Latite is considered a variety of trachyandesite containing as much sanidine as plagioclase.
Trachyandesites are lava forming thick flows and peaks, very common in Auvergne. Volvic stone is a trachyandesite produce by the Puy de la Nugère which has been used extensively in construction (Clermont-Ferrand cathedral) and as a support for enamelling, while sancyite is a trachyandesite with sanidine phenocrysts that found it on the crests of Puy de Sancy (Mont Dore).
