Hidalgoite

Hidalgoite, PbAl3(AsO4)(SO4)(OH)4, is a rare member of the beudantite group and is usually classified as part of the alunite family. It was named after the place where it was first discovered, the Zimapán mining district, Hidalgo, Mexico. At Hidalgo where it was initially discovered, it was found as dense white masses in alternating dikes of quartz latite and quartz monzonite alongside other secondary minerals such as sphalerite, arsenopyrite, cerussite and trace amounts of angelsite and alamosite, it was then rediscovered at other locations such as Australia where it occurs on oxidized shear zones above greywacke shales especially on the anticline prospects of the area, and on fine grained quartz-spessartine rocks in Broken Hill, Australia. Hidalgoite specimens are usually associated with copper minerals, clay minerals, iron oxides and polymetallic sulfides in occurrence. Hidalgoite is categorized under the trigonal crystal system and R3m space group and can be denoted by the H-M symbol (32/m). Physical properties of hidalgoite include its gray white to light gray color, a white streak, specific gravity of 3.96 and a hardness of 4.5. Hidalgoite specimens are usually translucent to sub opaque, and the brittle nature of mineral produces conchoidal fractures. It has an earthy luster.