CATION ORDERING AND STRUCTURAL DEFORMATIONS IN PECTOLITE HNaCaSi3O9 – SERANDITE HNaMn2Si3O9
I. V. Rozhdestvenskaya1, V. A. Vasilieva2
1St. Petersburg State University, St. Petersburg, Russia
2Karpinskii All-Russian Research Geological Institute, St. Petersburg, Russia
Keywords: pectolite, serandite, single crystal X-ray analysis, isomorphism
Abstract
Using the X-ray diffraction analysis, the structures of the pectolite-serandite series with the general formula HNaCa2–xMnxSi3O9, are studied where 0 < x < 2, with x = 0.02, 0.14, 0.39, and 1.17. The Mn2+ cations mostly occupy the M2 site (0.02, 0.14, 0.34, and 0.90 apfu). Here <M1–O> = 2.367–2.369 Å decreases down to 2.355 Å; <M2–O> decreases from 2.355 Å to 2.239 Å. The lengths О3–О4 = 2.47–2.49 Å, bond lengths H–O3 = 1.07–1.24 Å and H–O4 = 1.44–1.32 Å. For <M1–O> and <M2–O> of about (Mn2+ + Fe2+) ≈ 1 a turning point is noted in the graph. The a, b, c, and β parameters decrease linearly.
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