Recent sediments with distinct signs of hydrothermal alteration sampled in the Hess Deep(Galapagos Ridge, East Pacific Rise) contained a piece of ash-gray rock, which differed from other rock fragments by degree of consolidation, conchoidal fracture, and had properties of asbestos. Our studies found that the sample represented mixture of asbestos-like pyroxene of diopside-hedenbergite composition, amphibole of tremolite composition and a new mineral, which basic structure consisted of bands of triple pyroxene chains with the radical [Si6O16]. The latter can be regarded as intermediate between amphiboles and layered silicates. Also in some parts of the sample presence of trioctahedral vermiculite-chlorite was indicated. Genesis of the studied asbestos rock is considered from the standpoint of high-temperature hydrothermal-metasomatic alteration of sediment by post-magmatic mineralized halide solutions.

Supplement to: Rozanova, Tamara V; Drits, Victor A; Dmitrik, A L (1978): Hydrothermal pyroxene-amphibole-asbestos rock from the Hess Deep (East Pacific Rise). Litologiya i Poleznyye Iskopaemyye (Lithology and Mineral Resources), 13(5), 3-16