This is a really wonderful US phenacite from Mount Antero in Colorado. It features two separate twinned phenakite crystals, each about 12mm. They are rhombohedra modified by prism faces. Typical of Mt. Antero, the rhombic faces show stepping while the prism faces are striated. The crystals are a little etched and coated with tiny, specular, hexagonal, hematite plates and a light brown micro, maybe huebnerite. Overall size is 2 x 3 x 3.5 cm.