A Zinc Arsenate Hydroxide with formula: Zn2AsO4(OH). The hardness is 3.5.
Very popular among fluorescent mineral collectors because it’s bright green fluorescence under short and long UV light, as you can see from the picture.
This material comes from the Mapimi mines, Mexico: Is not easy to cut and polish due to his low hardness and brittle fibrous structure. In fact you will find very few cut stones in the market.