• journal_title：Mineralogical Magazine
• Contributor：F. Cámara ; E. Sokolova ; F. C. Hawthorne
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2011.075.6.2755
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：75
• issue：6
• firstpage：2755
• section：Articles

Rinkite, ideally Na₂Ca₄<em>REEem>Ti(Si₂O₇)₂OF₃, is a common mineral in alkaline and peralkaline rocks. The crystal structures of five rinkite crystals from three alkaline massifs: Ilimaussaq, Greenland; Khibiny, Kola Peninsula, Russia and Mont Saint-Hilaire, Canada, have been refined as two components related by the TWIN matrix (−1 0 0, 0 −1 0, 1 0 1) (Mo-<em>Kem>α radiation). The crystals, <em>aem> = 7.4132–7.4414, <em>bem> = 5.6595–5.6816, <em>cem> = 18.8181–18.9431 Å, β = 101.353–101.424(2)°, <em>Vem> = 776.1–786.7 ų, space group <em>Pem>2₁/<em>cem>, <em>Zem> = 2, <em>Dem>_calc = 3.376–3.502 g cm⁻³, were analysed using an electron microprobe subsequent to collection of the X-ray intensity data. Transmission electron microscopy confirmed the presence of pseudomerohedral twinning in rinkite crystals. The crystal structure of rinkite is a framework of TS (titanium silicate) blocks. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block in rinkite exhibits linkage and stereochemistry typical for Group I (Ti = 1 a.p.f.u.) of Ti disilicate minerals: two H sheets connect to the O sheet such that two (Si₂O₇) groups link to the <em>transem> edges of a Na polyhedron of the O sheet. The crystal chemistry of rinkite and nacareniobsite-(Ce) is discussed.