DISCOVERY OF AEGIRINE AS A VAPOR-PHASE SUBLIMATE AT TORFAJöKULL CALDERA, LANDMANNALAUGAR, ICELAND

Landmannalaugar is situated in the large, rhyolitic Torfajökull Caldera, the largest caldera in Iceland. Located in South Iceland, the 18-km diameter caldera is home to Iceland’s largest geothermal area. The region is anomalous because of its rhyolite to basalt ratio of 4:1, in contrast to the 1:5 seen at the other central volcanoes around the island.

A randomly examined piece of moderately indurated tuffaceous float, found in the streambed ~1 km west of the campground, revealed submillimeter, black prismatic crystals growing in vesicles. Tentatively identified as tourmaline, the sample was examined by the powder X-ray Diffraction technique at the University of North Carolina-Asheville (UNCA) which produced a positive identification of aegirine (acmite). An upcoming Scanning Electron Microscope examination at the UNCA lab will determine the chemical composition of the sample.

Evidence for gas-phase aegirine is rarely observed although it sometimes precipitates by leaching silica from the glass walls of the gas-collection equipment. It suggests an eruption temperature of 630º-700º C.

Efforts will be made to locate the source of the sample upon a return trip to Landmannalaugar.