This is a rare hydrated magnesium, uranium phosphate, in this case occurring on a nicely contrasting limonite matrix. The crystals are SHARP lustrous, vividly hued lemon yellow in color; growing up to .7 cm across. Truly incredible color! These were found in the mid 90s in a special project worked in part by collectors associated with one of Australis's museums. I have not seen but 3 pieces this good turn up again since the 90s.