Rosasite is a blue to blue-green carbonate mineral with the chemical formula (Cu, Zn)2(CO3)(OH)2 named after its type locality, the Rosas Mine in Sardinia, Italy. It is a secondary mineral found in oxidation zones of copper-zinc deposits, and its copper:zinc ratio is approximately 3:2. It is similar to, and associated with the mineral aurichalcite but can be distinguished by its hardness: rosasite has a Mohs hardness of 4.5 whereas aurichalcite’s is only 2. Rosasite crystals may form encrustations on matrix, or mammillary or botryoidal forms. Spherical aggregates may also occur.
1: Botryoids of rosasite and rosasite-included calcite crystals on limonite matrix from Ojuela Mine, Mapimi, Durango, Mexico. Source: irocks.com
2: Velvety botryoids of rosasite on a limonite matrix. From same locale as image 1, source: irocks.com