Polished specimen of margarodite pseudomorph after a large topaz crystal from one of the greisen-like (pseudogreisens, as I fondly call them) hydrothermal veins in Old Mine Park, Trumbull, Connecticut. The topaz crystal has been completely altered to a porcellaneous mixture of micas. It is interesting to note that XRF analyses of this material performed by the photographer have indicated that samples of pseudomorphosed topaz from Trumbull show detectable amounts of both Rb and Sr, while samples of topaz from hydrothermal veins that do not show signs of alteration only contain detectable amounts of Rb. I theorize that substitution of Ca for Sr in the margarite contained in this sample is responsible for its elevated strontium concentration. Since samples from other hydrothermal veins contain little margarite, they do not show elevated levels of Sr.
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