A rich miniature of botryoidal dark forest green Cornwallite lining a deep cavity in white Quartz from Mammoth mine in the Tintic District of Juab County, Utah, USA. Cornwallite is a rare copper arsenate, named for the county of Cornwall and in this specimen displays an attractive velvet textured surface with a silky lustre. Also adhering to the Quartz is a grey mixture of undefined sulphides with occasional Limonite. This is a beautiful and rich miniature of Cornwallite from the Mammoth mine, Utah.