Mineralpedia Details for Margaritasite
Named for the co-type localities of the mineral at the Margaritas No. 1 and Margaritas No. 2 mines in Chihuahua, Mexico. The Margaritas mines are the only locality for Margaritasite and it occurs there as filling pores and casts of phenocrysts in felsic volcanic tuffs that have been altered by hot hydrothermal fluids. Margaritasite is strongly radioactive.
Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/margaritasite.pdf
Margaritasite from Margaritas mine, Sierra Peña Blanca, Chihuahua, Mexico
Tiny bright, gold finch yellow crystals to about 0.75mm.