All minerals before and after exposure to simulated Venusian conditions in the GEER for 60 days. The image was acquired by the on-site NASA GRC photographer using a NIKON camera. Most minerals became visibly darker after exposure, except calcite and magnesite. (A) Calcite: CaCO₃; (B) Magnesite: MgCO₃; (C) Siderite: FeCO₃; (D) Phlogopite: KMg₃AlSi₃O₁₀(F,OH)₂; (E) Muscovite: KAl₂(AlSi₃O₁₀)(F,OH)₂; (F) Brucite: Mg(OH)₂.