This stone is a medium to course-grained orthoquartzite. It is composed almost entirely of quartz grains that range from silt size to small pebbles as much as half an inch (1 cm) across. Minor constituents include small grains of feldspar, muscovite, magnetite and zircon.Small flakes of hematite are also present, and thin films of red opaque material, which is probable hematite, commonly coat quartz grains and give the rock a reddish cast.

The Flathead Quartzite has chemical and physical properties that appear to make it suitable for use as dimension stone and crushed and broken stone. It consists almost entirely of quartz grains cemented by overgrowths of clear quartz and the rock is hard, tough, massive, compact, and extremely resistant to chemical and mechanical weathering. The rock is pale gray, white, and light reddish gray, and the surface weathers to a pleasing tan, brown, or maroon. In places the quartzite is decoratively streaked by narrow red and purple bands.

The rock breaks down naturally into large and small squarish blocks. Many of the blocks appear to be suitable for use as rough dimension stone. The Flat head could probably be quarried to produce crushed and broken stone. The quartzite is the most chemically inert of all the rocks in the Wolf Creek area. Crushed material screened to the proper size would make excellent concrete aggregate. Most of the Flathead is composed of quartzite that contains some impurities and in which the constituent grains of quartz are coated with films of red iron oxide. This rock is estimated to consist, however, of 95 to 98 percent quartz. The Flathead quartzite is hard, compact, and dense and does not break down naturally into loose sand particles.

Reference Cited: Rocks and Mineral Resources of the Wolf Creek Area, Lewis and Clark and Cascade Counties, Montana USGS Bulletin No. 1441 Compiled by Robert George Smith.