Locally abundant specimens of large and well-crystallized wavellite, fluellite and minyulite are present in quartz crystal-lined vugs, along with other minerals including native selenium, and a suite of associated phosphates.
A carbonaceous and sulfide-bearing shale horizon just barely exposed at the bottom of the northernmost pit of the Willard mine contains excellent wavellite, fluellite and minyulite. Other minerals present in attractive, smaller crystals or coatings include cacoxenite, crandallite, dufrenite, gypsum, jarosite, native selenium and strengite/variscite.
It is the site of the first discovery of minyulite in Nevada; it has produced the world's largest crystals of fluellite and perhaps also minyulite; and it has furnished what are by far the finest quality specimens of wavellite, fluellite and minyulite ever discovered in the state.
The Willard mine is the source of the best minyulite found in Nevada; some truly remarkable pieces have been produced.
Minyulite, like fluellite, is a paragenetically late mineral, and may occur either alone, or with botryoidal strengite/variscite or finely crystallized wavellite spherules.
It may thus be suggested that where both wavellite and fluellite have been found, the third member of the association, minyulite, may also very likely be present.
At this locality in the spring of 1996, sincosite, a rare vanadium phosphate, was found associated with minyulite and hessite in gold-bearing siltstone of the lower Cambrian Deadwood Formation.
Then we would carefully pry open the rock and discover beautiful clusters of sincosite and sprays of minyulite lining the tight vugs in the rock.
Elements Gold Au Silver Ag Tellurides Hessite [Ag.sub.2]Te Fluorides Fluorite Ca[F.sub.2] Carbonates Azurite [Mathematical Expression Omitted] Calcite CaC[O.sub.3] Malachite [Mathematical Expression Omitted] Phosphates Minyulite K[Al.sub.2][(P[O.sub.4]).sub.2](OH,F)[center dot]4[H.sub.2]O Sincosite [Mathematical Expression Omitted] Sulfates Barite BaS[O.sub.4] Gypsum CaS[O.sub.4][center dot]2[H.sub.2]O MINERALOGY
Minyulite commonly occurs with sincosite as beautiful white, acicular, radiating sprays averaging 3 mm but rarely up to 1.5 cm.