Cerite, (Ce,La,Nd,Ca) 9 (Fe (super 3+) ,Mg,Al)(SiO 4 ) 6 (SiO 3 OH)(OH) 3 , rhombohedral, a = 10.779(6), c = 38.061(7)angstrom, Z = 6, space group R3c, is nearly isostructural to whitlockite, Ca 9 Mg(PO 4 ) 6 (PO 3 OH). R = 0.032 for 1711 independent reflections. Cerite is related to a large family of "bracelet and pinwheel" structures derived from glaserite. Rods of two kinds run parallel to the c-axis. It is suggested that cerite probably has F (super -) analogues, and is related to a substantial family of rare earth silicates with rhombohedral structures such as cappelemite, okanoganite and steenstrupine.--Modified journal abstract.

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