SPINELS AS MARKERS OF FORMER MINERALS IN ONE THIN-SECTION OF KOMATIITE SAMPLE

Two types of feature shown by cruciform spinels in one thin section of a Munro komatiite sample are described. In the first one, spinels occ ur within the contours of a former mineral and draw a net which may ha ve been guided by the crystallographic elements of the above mineral. In the second type, spinels are present along lines in thin bands of f ormer clinopyroxenes now altered to amphiboles occurring in a former o rthopyroxene now altered to anthophyllite and chlorite. Such textures may be used for identification of earlier minerals, especially orthopy roxenes, the role of which appears primordial in komatiite's genesis.