Crystal chemistry of synthetic Ca2Al3Si3O12OH-Sr2Al3Si3O12OH solid-solution series of zoisite and clinozoisite

Coexisting solid-solution series of synthetic zoisite-(Sr) and clinozoisite-(Sr) were synthesized in a 1 M (Ca,Sr)Cl-2 solution at 2.0 CiPa, 600 degrees C for 6 days in a piston cylinder press. Solid solutions were synthesized from X-Sr(Zo) = Sr/(Ca + Sr) = 0.06 to 1 and X-Sr(Czo) = 0.08 to 0.5 in zoisite and clinozoisite, respectively. The products were characterized with SEM, EMP, and powder-XRD. Zoisites form crystals up to 30 pm in size. Lattice parameters of zoisite increase linearly with increasing Sr content. For synthetic zoisite-(Sr) lattice parameters are a = 16.3567(5) angstrom, b = 5.5992(2) angstrom, c = 10.2612(5) angstrom, and V= 939.78(7) angstrom(3) in space group Pnma. Volume of clinozoisite (P211m) increases with increasing X-Sr(Czo), but the lattice parameter a collapses, and b, c, and beta have a discontinuity at X-Sr(Czo) approximate to 0.25. The decrease in angle P of clinozoisite results in compression of M3 and T3 polyhedra and increase of the A2 polyhedron. A1-O7 distance of 2.12 angstrom in clinozoisite is extremely short at X-Sr(Czo) approximate to 0.25, but with further Sr incorporation on A2 this distance relaxes quickly to 2.24 angstrom, combined with a torsion of T3. In zoisite, Sr incorporation leads to an opposite movement of neighboring octahedral chains parallel a and causes changes in the linked T3, and angle 05-T3-O6 increases with X-Sr from 96.3 to 101 degrees. The intra-crystalline distribution of Sr shows that A2 is the favored position and continuous incorporation on A1-position starts above X-Sr(Zo) approximate to 0.35 for zoisite and above X-Sr(Czo) approximate to 0.45 for clinozoisite.