THE CRYSTAL STRUCTURE OF β-CaMg2(SO4)3, A MINERAL PHAS

详细信息   p://canmin.geoscienceworld.org/content/48/6/1469.full">在线全文   p://canmin.geoscienceworld.org/content/48/6/1469.full.pdf">PDF全文下载

• journal_title：The Canadian Mineralogist
• Contributor：Sergey V. Krivovichev ; Elena P. Shcherbakova ; Tursyn P. Nishanbaev
• Publisher：Mineralogical Association of Canada
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.48.5.1469
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：48
• issue：6
• firstpage：1469
• section：Articles

摘要

<p id="p-1">The crystal structure of β-CaMg₂(SO₄)₃ (“perkovaite”), an anhydrous Ca–Mg sulfate from coal dumps of the Chelyabinsk coal basin, in Russia, was solved by direct methods and refined to an R₁ value of 0.054, calculated for the 1808 unique observed (|F_o| ≥ 4σF) reflections and 234 refined parameters. The compound β-CaMg₂(SO₄)₃ is hexagonal, P6₃, a 16.581(1), c 7.348(6) Å, V 1749.5(14) Åp>3p>. It is a polymorph of CaMg₂(SO₄)₃, but in contrast to synthetic α-CaMg₂(SO₄)₃ [P6₃/m, a 8.3072(4), c 7.3057(8) Å], β-CaMg₂(SO₄)₃ has a doubled a unit-cell parameter. The structure is a three-dimensional framework consisting of two types of rods extending parallel to the c axis and alternating in the (001) plane. Rods of type I are based upon dimers of face-sharing MgO₆ octahedra that are linked by sharing corners with SO₄ tetrahedra. Rods of type II consist of CaO₈ polyhedra linked by SO₄ tetrahedra. The structures of β-CaMg₂(SO₄)₃ and synthetic α-CaMg₂(SO₄)₃ have the same basic topology, but differ in the displacement of respective atomic groups. The formation of the two polymorphs is probably due to different thermodynamic conditions, in particular, the temperature regime. It can also be possible that β-CaMg₂(SO₄)₃ is a product of secondary changes of CaMg₂(SO₄)₃ under atmospheric conditions. p>