Mineral
Calcofanita
(Zn,Mn²⁺)(Mn⁴⁺,Mn³⁺)₃O₇·3H₂O · Óxidos
Chalcophanite is a supergene hydrated manganese–zinc oxide. It can be described as a partly oxidised manganese-oxide framework, stabilised by zinc, with water incorporated in the structure. It forms crusts, botryoidal aggregates and stalactitic structures, with dull lustre and colours from brown to black. In its formula "(Zn,Mn²⁺)(Mn⁴⁺,Mn³⁺)₃O₇·3H₂O", the parentheses denote substitution: a crystallographic site may be occupied by more than one element. In the first group "(Zn,Mn²⁺)" the site is normally filled by zinc (Zn), with partial substitution by Mn²⁺. In the second group "(Mn⁴⁺,Mn³⁺)₃" there are three manganese positions that may host Mn⁴⁺ or Mn³⁺, coexisting in the crystal. The "O₇" are the oxygens forming the oxide framework, followed by three molecules of structural water "·3H₂O" integral to the mineral structure.
Etymology
From Greek "chalkos" (copper) and "phainesthai" (to appear), alluding to its visual resemblance to copper minerals.