Specimen data for Sekaninaite

Tom Mortimer catalog number: 1682

Identification method: EDS analysis. Sekaninaite forms a series with Cordierite. Sekaninaite is the Fe rich end member. Cordierite is the Mg rich end member. The interpretation of a 2009 EDS analysis by Kerry Day (from his EDS plot below) suggested that this Franklin, NH material is close to the mid-point of the Cordierite-Sekaninaite series, slightly on the Fe rich side. The K and Ca peaks were judged to be surface contaminates on the specimen.

A polished grain EDS analysis (BC457) clearly indicated Fe > Mg. The chemistry indicated by this BC457 analysis is:
(Fe_1.13,Mg_0.86)Al_3.87Si_4.51O₁₈ , normalized for 18 oxygen. The Fe₂O₃ of the analysis was converted to FeO for this formula to agree with that given for sekaninaite.
Webmineral.com gives an empirical formula for sekaninaite as : (Fe_1.5,Mg_0.5)Al₄Si₅O₁₈.
A sample grain from a Harvard University collection, Franklin Dam specimen (#118874) was analyzed.
This indicated a chemistry of (Fe_1.31,Mg_0.67)Al_3.65Si_5.16O₁₈ , normalized for 18 oxygen, in reasonable close agreement with the BC457 analysis.
Harvard BC471 EDS analysis (BC471)