Quartz varieties of the SQC group crystal deposits

The gitological study of the quartz crystalliferous deposits of the SQC group, under the Itremo domain, Madagascar, was carried out under a cartographic, petrographic and structural approach. The study shows that these deposits are related to the second phase of deformation (D2) involving both folding and fracturing during the Pan-African orogeny. Quartz crystals are contained in tension cracks in the form of quartz pegmatites, veins and veins that are concordant or discordant to the foliation of the metasediments. The formation process of the mineralized facies is derived from the circulation of hydrothermal fluids, of low temperature, and sometimes with a probable meteoric component. The automorphic and transparent quartz crystals form crystalline sprays within multi-centimetric to metric geodic cavities. They show a more or less pronounced Dauphiné habitus and some rare plagiarism. The different varieties of crystals are piezoelectric quartz, hyaline quartz, hematoid quartz, ghost quartz, hair quartz and amethyst.