Abstract

Carlosturanite, ideally M21[T12O28(OH)4](OH)30 · H2O, is a water and magnesium-rich, silicon-poor serpentine-like asbestiform mineral. TEM techniques revealed the fiber texture, which consists of randomly rotated fibers approximately 1000Å in cross section intermixed with smaller chrysotile fibers. TEM also permitted the unit cell to be found and a plausible structural model to be proposed.

The model is based on the ideal structure of serpentine, from which carlosturanite differs by the presence of infinite rows of vacancies in tetrahedral sites. As a result, carlosturanite is a chain silicate, characterized by the presence of triple chains. These chains are related to the four-repeat single crankshaft chains of haradaite and could be formed by linking three haradaite chains. This model explains the physical and chemical properties of the mineral.

Starting from the carlosturanite arrangement, a comprehensive discussion of the possible carlosturanite-like phases is given and the family name inophites is proposed. Inophites belong to a polysomatic series, SnX, resulting from combination of serpentine S modules, with composition M3T2O5(OH)4, and of X modules, with composition M6T2O3(OH)14 · H2O. Evidence of the existence of the S4X, S6X and S7X structures as fault lamellae within carlosturanite, S5X, is given.

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