Brochantite is a relatively common secondary copper sulfate mineral frequently found as pseudomorphs after Malachite or Azurite, however, well-formed crystals like this gorgeous thumbnail are the exception. Sharp, well crystalized examples are best known from the now closed Milpillas Mine in Mexico. This fine thumbnail features several deep green Brochantite crystals to 2 cm arranged in a stellate pattern with most of the divergence from the center of the piece. It's a super aesthetic thumbnail example from the Bill and Anne Cook collection with a Crystal Cellar label. These came out about 2013-15 and are now regarded as some of the finest crystals of the species. This is a rich, large and showy thumbnail specimen.