The NSS Bulletin - ISSN 1090-6924
Volume 57 Number 2: 85-90 - December 1995

A publication of the National Speleological Society

Metatyuyamunite from Spider Cave, Carlsbad Caverns National Park, New Mexico
Victor J. Polyak and Cyndi J. Mosch

Abstract

Metatyuyamunite [Ca(UO2)2(VO4)3 3-5H2O], a hydrated uranyl vanadate, has precipitated as decimicron to millimeter-sized crystals in Spider Cave, Carlsbad Caverns National Park. Crystals are canary yellow and plate-like; they commonly consist of laths shaped like "playing cards" standing upright. Metatyuyamunite occurs as a druse in association with botryoidal opal coatings. X-ray diffraction and optical and scanning electron microscopy were used to identify metatyuyamunite. Tyuyamunite was not found to be present in the samples analyzed. The metatyuyamunite was found to have unit-cell dimensions of a = 10.397(4)Å, b = 8.403(2) Å, c = 16.692(12) Å. Spider Cave has developed within dolostones and siltstones of the Yates Formation. Uranium and vanadium compounds were probably concentrated and deposited along an oxidation-reduction front during the (sulfuric acid) dissolution of bedrock which formed the cave. Association of metatyuyamunite with secondary opal on breakdown blocks, floor deposits, and speleothems indicates that metatyuyamunite mineralized from vadose solutions after speleogenesis and lowering of the water table.

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