Tiny brown fillowite crystals in rock cavity. From the Fillow Quarry, Branchville, Redding, Connecticut. Field of view is 1.2 mm. (Photo courtesy Harold Moritz; unauthorized reproduction is prohibited.)

Formula: Mn2+Na8(Ca4Na4)(Mn2+Fe2+)43(PO4)36 Monoclinic


Fillowite is a rare mineral found as yellowish to reddish brown granular masses in complex granitic pegmatites.

FLORENCE COUNTY: Fillowite is a component of light brown to tan nodules in the complex pegmatites in sec. 22 T.39N. R.17E., near Fern. The fillowite forms rims on apatite. Microprobe study shows it to be compositionally very close to the pure manganese-rich end member (Falster, Simmons and Moore, 1988).