This striking, vivid blue cabinet specimen was formerly in the collection of well-known collector Marion Stuart. Her accompanying card and unique plastic engraved label identify the mineral as leightonite, an ultra-rare copper sulfate, which typically has the crystal form seen on this piece. The Type Locality is the Chuquicamata Mine of Chile. Krohnkite is another ultra-rare copper sulfate, with similar color from Chuquicamata, but usually forms in lamellar growth of curved crystals in parallel bundles. Another dealer had this specimen X-rayed in May, 2008 and the report is included with the specimen. It was krohnkite on the rhyolite matrix, but in a very uncommon botryoidal/crust-like form. This specimen exhibits the most intense teal blue color I have ever seen in a natural mineral specimen and has great translucence. And the variation in blue color, in itself, is very noteworthy.