Rietveld refinement of chromian clinochlore from the chromitites of Golyamo Kamenyane serpentinite (Eastern Rhodopes)

The structure of a disordered IIb chromian clinochlore from the chromitites of Golyamo Kamenyane serpentinite (Eastern Rhodopes) was studied using Rietveld refinement techniques and powder X-ray diffraction (CuKα, 3–100° 2Θ in 0.013° 2Θ increments). The refinement in space group C–l yielded the following lattice parameters: a = 5.299(2) Å, b = 9.2625(5) Å, c = 14.4726(6) Å, α = 90.103(7)°, β = 97.191(13)°, γ = 90.320(11)°, and cell volume of 704.69(21) Å3. The structure of the studied mineral is characterized by a semi-random stacking of adjacent chlorite layers creating a situation in which not all atoms positions could be precisely located. Despite this limitation, the crystal chemical plausibility of the final structural model could be achieved due to the fact that most of the atomic positions (all octahedral cations and anions) repeat at intervals of ±b/3 and could be uniquely determined. The type of structural information that can be derived from the test compound and similar structurally related materials by applying the Rietveld method is discussed and ways to achieve this are considered.