Icelandite is a type ofvolcanic rock, anandesite that is enriched iniron but deficient inaluminium (< 16.5%Al2O3).[1][2] Icelandites are betweenrhyodacite andtholeiitic basalt in composition and containandesine,hypersthene andaugite, with asilica (SiO2) content greater than 60%.[3]
The name was coined by the BritishgeologistIan S. E. Carmichael (who later became professor at theUniversity of California, Berkeley) while working around 1960 on hisPhD thesis at aCenozoicvolcano near the parsonageThingmuli (Þingmúli) in EastIceland.[4] For continental cogenetic series of volcanic rocks it is generally the case that the concentration of iron decreases with increasing silica content, but at Þingmúli the opposite was true, leading Carmichael to the conclusion that the iron-richintermediate rock deserved its own name,icelandite.
With its elevated iron content and low aluminium content compared withcalc-alkaline andesite,[5] icelandite is assigned instead to thetholeiitic magma series.[2]
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