Abstract
Freudenbergite is shown to be monoclinic with unit-cell dimensions a = 12.305 Å, b = 3.822 Å, c = 6.500 Å, β = 107.30°, diffraction symbol 12/ m 1 C …, and unit-cell contents approximating to (Na,K) 2 (Ti,Nb) 6 (Fe III ,Si) 2 (O,OH) 18 . It exhibits slight structural resemblance to pseudobrookite. A 15 R -högbomite polytype is associated with freudenbergite at Katzenbuckel.

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