Growth zoning of ZnS-CuZn₂InS₄ solid solutions

(In concentration map)

(Cu concentration map)

In an economic sense, the most important indium mineral from the Toyoha mine is an unnamed zinc-indium sulfide, CuZn₂InS₄, which makes solid solutions with sphalerite, ZnS. These two images show concentration of indium, and of copper in the solid solution. Growth zoning in a single crystal of the solid solution is obvious. Actual width of the mapped area is 0.3mm.

If we express four molecules of sphalerite (4ZnS) as Zn₄S₄, and then substitute two atoms of zinc (ZnZn) with a pair of copper and indium (CuIn), then we get the chemical formula of the zinc-indium sulfide, CuZn₂InS₄. An incomplete substitution would result in a solid solution of intermediate composition between the two phases. The red zones of highest indium concentration in the above image correspond to the zinc-indium sulfide, and the dark zones to sphalerite. Actually the chemistry of the solid solution is a bit more complex, because of other kinds of substitutions, such as Zn with Fe, Cd or Mn.

These two images give a perfect evidence of the substitution: ZnZn with CuIn.

Seeing is believing.