Specific gravity: 5.91 calculated
Colour: Greyish yellow, olive-green, brownish black
Luminescence: Non-fluorescent in short wave and long wave ultraviolet light
Andymcdonaldite is a relatively new mineral, approved 2019 and to date (April 2022) reported only from the
At the type locality, the Wildcat Project, Detroit Mining District, Juab County, Utah, USA, andymcdonaldite occurs as thin fracture coatings on gold-, tellurium- and bismuth- rich jasperoid, and as partial matrix-fillings of brecciated jasperoid.
One area of jasperoid boulders contains exceptionally high concentrations of metals (gold 301 ppm, tellurium 3800 ppm, bismuth 1935 ppm) and this is where tellurium oxysalt mineralisation has been found.
Andymcdonaldite occurs sparingly as thin yellowish-brown to brownish-black coatings on freshly broken rock fractures. Associated minerals include abundant white to colourless or pale tan carlfriesite, crystals of tlapallite, beudantite, beyerite, brochantite, clinobisvanite, eckhardite, frankhawthorneite, gold, hedyphane, khinite, malachite, mcalpineite, paratellurite, tellurite, tellurium and xocolatlite. Fischesserite, iodargyrite, naumannite and petrovskaite are probably also present.
The andymcdonaldite, carlfriesite, and other oxysalt minerals at Wildcat likely formed from oxidation of primary tellurium and/or telluride phases, during late-stage, weathering-related oxidation. Remnant tellurium in rare partially oxidised jasperoid is closely associated with paratellurite and tellurite. Intermediate oxidation zones are dominated by carlfriesite with minor tlapallite. Closer to the original surfaces of jasperoid boulders, carlfriesite is absent but andymcdonaldite and xocolatlite are present. In places, andymcdonaldite encrusts carlfriesite. On the original exposed surfaces of jasperoid boulders, andymcdonaldite and xocolatlite are largely missing but black-coloured manganese-bearing oxides are present (CM 58.1.85-97).
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