The alteration of olivine in basaltic and associated lavas

Abstract

Olivines which cool under oxidizing conditions exsolve iron oxides at high temperature, and at low temperatures break down to essentially chloritic materials. Olivines which cool under non-oxidizing conditions alter at intermediate temperatures to complex assemblages of chlorite and interstratified phyllosilicates containing a smectite. Alteration under oxidizing conditions at low temperature, probably below 140° C, produces “iddingsite”, an orientated assemblage of goethite and interstratified phyllosilicates also containing a smectite.