Dark reddish-brown altered (metamict) grayite mass in fine-grained granite. Field of view is 1.2 cm. From Koss Pit, Marathon County, Wisconsin. Collected by Tom Buchholz. Specimen is in the University of Wisconsin–River Falls collection. (Photo by W. Cordua.)

Formula: (Th,Pb,Ca)PO4.H2O Hexagonal


Grayite is a rare member of the rhabdophane group found in rare element pegmatites. Minerals such as grayite often show up as anomalous “specks” that are recognized only by master mineral collectors, and whose identity must be verified by advanced analytical techniques.

DODGE COUNTY: Tiny grains of grayite-like mineral were seen in pegmatites cutting quartzite in the Michels Materials Waterloo Quarry, NE sec. 33 and NW sec. 34 T.9N. R.13E. (Buchholz et al. , 2003)

MARATHON COUNTY: Grayite has been documented as occurring in pegmatites in the Koss Pit, a large “rotten granite” quarry in the SW sec. 2 T.27N. R.5E. It is also tentatively noted from the Maguire Pit in the Ladick Quarry Complex (sec. 19 and 20 T. 27N. R.6E.) (Buchholz and Simons, 2002; Buchholz et al., 2004).