Geology and Mineralogy
The lava historically erupted from Izalco consists of vesicular vitrophyric olivine basalts. Izalcos formation was preceded by Fumorolic activity in 1658, before Izalco was born in 1770. Today, Izalco experiences only fumarolic activity in the form of rainwater seeping into the volcano and contacting hot rocks, rather than steam emissions from underground gases. The fumarole deposits of the volcano are noted as sources for several rare minerals. It is the type locality for the copper vanadium minerals: bannermanite, blossite, fingerite, howardevansite, lyonsite, mcbirneyite, stoiberite and ziesite.
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