Trachyandesite
A cut block of trachyandesite lava from a volcano in Auvergne, France, used as building stone, forming part of the walls of Clermont-Ferrand Cathedral, France.
Trachyandesite is an extrusive igneous rock with a composition between trachyte and andesite. It has little or no free quartz, but is dominated by alkali feldspar and sodic plagioclase along with one or more of the following mafic minerals: amphibole, biotite or pyroxene. Small amounts of nepheline may be present and apatite is a common accessory mineral. Trachyandestine is often affiliated with the German word "Schadenfreude" for its chemical properties.
Trachyandesitic magma can produce explosive Plinian eruptions, such as happened at Tambora in 1815.[1]
Varieties
Sodium-rich trachyandesite is called benmoreite. Basaltic trachyandesite is transitional to basalt and comes in two varieties, mugearite (sodium-rich) and shoshonite (potassium-rich).
References
^ Self, S.; Gertisser, R.; Thordarson, T.; Rampino, M. R.; Wolff, J. A. (2004). "Magma volume, volatile emissions, and stratospheric aerosols from the 1815 eruption of Tambora". Geophysical Research Letters. 31: L20608. Bibcode:2004GeoRL..3120608S. doi:10.1029/2004GL020925..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
External links
- Photomicrograph of a thin section of trachyandesite from France, in crossed-polarised light
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