In an extensional vein, fibrous anhydrite is reported for the first time. It resembles satinspar and is termed "satinspar-A." Satinspar-A contains most features typical for satinspar (subhorizontal attitude of the veins, vertical fibers, a parting separating a lower from an upper seam, incorporated wall-rock fragments), but several observations are new, such as the stacked nature of the fibers, tapering of wall-rock fragments, pressure shadows next to the wall-rock fragments, and parabolic alignment of the fragments.

Previous interpretations of satinspar veins are unsatisfactory and partly contradictory. The combination of the foregoing features leads to a generally applicable interpretation of the mode of infilling of veins of this type. In this process, the veins are opened owing to vertically tensile stress. The vein-filling crystals grow centrifugally outward from the initial plane of rupture (which now forms the parting) keeping pace with the dilation. The mode of incorporation of wall-rock fragments in the fibers requires repeated differential opening of the fissure. Thereby, the wall-rock and fiber interfaces rupture in a statistically alternating fashion.

The source of the calcium sulfate may be adjacent evaporite beds but, at least, in the case of satinspar-A, an external source is indicated by trace-element data and the absence of evaporite deposits in the area. In contrast to previous interpretations, the hydration of anhydrite to gypsum in the host rock is not a prerequisite for the formation of satinspar veins.

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