Depositional environment for metatyuyamunite and related minerals from Caverns of Sonora, TX (USA)

A new mineral association composed of metatyuyamunite, celestite, opal and several minor crystalline phases has been identified in the Caverns of Sono ra (Texas). The minerals were identified by means of X-ray diffractometry a nd optical and scanning electron microscopy. The main component of this ass ociation is metayuyamunite, a uranyl vanadate mineral that appears as aggre gates of sub-millimeter platy-like crystals that are often covered by botry oidal opal coatings. The orthorhombic unit cell of the Sonora metatyuyamuni te had parameters a = 10.418. b = 8.508, and c = 17.173 Angstrom. Opal and celestite formed either directly over the yellow crust or along the cracks that traverse the limy mud on which metatyuyamunite was precipitated. The s econdary uranium-vanadium minerals described herein were precipitated in th e final stages of cave development.