Rutile and topaz in Precambrian gneiss, Jefferson and Clear Creek Counties, Colorado

Disseminated rutile and major amounts of topaz have been identified in Precambrian topaz-quartz gneiss northwest of Evergreen, Colo. The rutile occurs in quartz-topaz-sillimanite gneiss that forms a stratigraphic unit which is 11 to 100 feet thick and is identified along strike for more than 7,000 feet. Three composite chip samples taken across this unit contain 2.2 to 4.2 percent of rutile, by weight, in grains averaging from 0.1 to 0.3 millimeter in size. The topaz content, by weight, in the same samples ranges from 23 to 67 percent.