Thorogummite replacing thorianite crystal. From the Rock Landing Quarry, Haddam Neck, Haddam, Middlesex County, Connecticut. Field of view is 2.05 mm. (Photo courtesy Harold Moritz; unauthorized reproduction is prohibited.)

Formula: (Th,U)(SiO4)1-x(OH)4x Tetragonal


Thorogummite is formed by the alteration of other thorium-rich minerals, such as thorite. IMA currently lists its status as a species as “doubtful.”

MARATHON COUNTY: Much of the thorite found in the pegmatites of the Stettin pluton have been altered, in part to thorogummite, forming masses as much as 10 cm across (Falster et al., 2000).
—Nodules of thorogummite have been found in the soils at several localities around the Stettin pluton. The nodules are reddish, 1 to 2 cm in diameter and are crystalline, not metamict. Localities described (all in T.29N. R.6E.) are: N 1/2 NW and SW SE sec. 27 and SW SE and NE NW sec. 28. (Vickers, 1956).
—Thorogummite was tentatively reported from the zircon mine in the SE SE sec. 22 T.29N. R.6E. (Sood, Myers and Berlin, 1980).

WOOD COUNTY: A metamict mineral occurring as “black, pitch-like reniform clumps” in a pegmatite dike at the Frederich Schill Quarry, NE of Vesper on the E side of Hwy 180, is tentatively identified as thorogummite (Buchholz,1999).