Analcime of the Mariinskoe deposit (Urals emerald mines, the Middle Urals): chemical composition and crystal structure
Zhitova E. S., Popov M. P., Zolotarev A. A. jr.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2017. V. 146. N 4. P. 111-120
The Cs-bearing (~ 3.5 wt % of Cs2O in average) analcime from the Mariinskoe deposit (the Urals Emerald Mines) occurs in well-formed tetragon-trioctahedron colorless or milky-white crystals from 1 to 7 mm in size. Most often the mineral overgrows on albite or phrenite and has the later hydrothermal origin. Single-crystal X-ray diffraction study revealed its cubic symmetry, space group Ia3d, a = 13.714(2) Å, V = 2579.0(6) Å3. Crystal structure was solved to R1 = 0.037 on the basis of 157 independent reflections with F > 3σ(F). The crystal chemical formula of analcime based on the refined site-scattering factors Na0.78[(H2O)0.92Cs0.08]Al1.08Si1.92(O5.78OH0.22) is in well agreement with the formula calculated on the base of electron-microprobe data: Na0.79[(H2O)0.95Cs0.05]Al0.98Si2.02(O5.86OH0.14). Substitution in the extra-framework part corresponds to the scheme Na+ + H2O = □ + Cs+. We revealed the optical anisotropy of cubic analcime which can be explained by the deficiency of water molecules.
Key words: analcime, cesium, crystal structure, Mariinskoe deposit, Urals Emerald Mines.