Geological characterization of lapilli in Gran Canaria island : a raw material used as a gas granular filter

Abstract

Lapilli is a pyroclastic material ejected by volcanoes (2-64 mm of grain size ). Lapillis from recent strombolian eruptions of Gran Canaria have been used as a granular filter for removing fine dust particles from gases and for heat exchange as well. The geological characteristics of these lapillis are: A) They come from ultrabasic geochemical composition magmas (<45% content of Si 02, and >3% ofNa2o+K20); B) Petrologic features indicate lapillis are mainly basanitic and nephelinitic in composition; C) Lapilli textures varíes from holohyaline ( l 00% of volcanic glass) to hypocrystalline (glass plus crystals), are black, slightly welded and very vesicular, consequently they have high porosity and penneability; D) Toe most interesting lapillis to be used as granular filters are of Upper Quaternary age ( < 300,000 years) because of their low weathering and cohcsiveness; E) Calculated reserves of this material in Gran Canaria are large, up to 350 million m3, but many of the recent volcanic eones are located in natural places protected by Law. However, the local demand of lapilli as raw material of granular filters ( <100 m3/year) could be satisfied with quarries now available.