Detailed mapping undertaken between 1982 and 1987 of 48 known jade outcrops located in the Cowell - Cleve area, and diamond drilling of 3 jade outcrops and 2 ornamental marble prospects, has identified many factors controlling nephrite formation. The country rocks are either Early Proterozoic Hutchison Group sediments, apparently derived by weathering from banded calc-silicate gneiss at the base of the Warrow Quartzite, or comprise Katunga Dolomite and carbonate facies of the ?Lower or Upper Middleback Jaspilite. In all cases, the nephrite host rocks are dolomitic marble and massive M1/M2 diopside. It appears that nephrite was formed by several mechanisms : - Metasomatism of dolomitic marble along D4 fractures. - Metasomatism of dolomitic marble along the margins of ?early D4 pegmatite. The pegmatite has also been metasomatised to produce two characteristic styles of hybrid pegmatite. Nephrite emplacement is not along the main set of D4 joints and dissolution planes. - Retrogression of massive M1/M2 diopside. Nephrite is often foliated, with a partly-sigmoidal S4 foliation interpretable in terms of simple shearing during D4, but with varying degrees of intensity and sense of movement.