• journal_title：European Journal of Mineralogy
• Contributor：Rodney Grapes ; Jörg Keller
• Publisher：E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.1127/0935-1221/2010/0022-1996
• journal_abbrev：Eur J Mineral
• issn：0935-1221
• volume：22
• issue：2
• firstpage：285
• section：Articles

Fe-dominant rhönite with between 25 and 28 wt% FeO (as total iron) occurs as a late crystallizing phase in tephrite and limburgite from the Kaiserstuhl volcanic complex, Upper Rhine Graben, Germany. Average compositions are: (K_0.05Na_0.40Ca_1.55)₂ (Mg_1.85Mn_0.03Fe²⁺_2.45Fe³⁺_0.66Al_0.09Ti_0.92)₆(Si_3.88Al_2.12)₆O₂₀ in tephrite and (K_0.01Na_0.58Ca_1.41)₂(Mg_1.93Mn_0.03Fe²⁺_2.26Fe³⁺_0.71 Al_0.17Ti_0.90)₆(Si_3.96Al_2.04)₆O₂₀ in limburgite. Mg/(Mg + Fe²⁺) ratios range between 0.40 and 0.49, and the Fe²⁺-rich rhönite can be classed as an unnamed Fe²⁺-dominant analogue of rhönite with XMg <0.5 as defined by Grew et al. (2008). Compared with other Fe²⁺-dominant rhönites in terrestrial and extraterrestrial rocks, the Kaiserstuhl compositions have less Ti and are richer in Si + (Na,K). The Kaiserstuhl rhönite coexists with subsilicic Al–Ti-bearing augite and titanian magnetite as in other basaltic occurrences of Fe²⁺-dominant and Mg-dominant rhönite, and is a quench phase in glass with liquidus temperatures of 1137–1068 °C.