Quarry Layers

Beneath a cover of soil, a thick, pink-tinted layer of Sioux quartzite covers the thin, red-colored lower layer of pipestone, the prized stone of many tribal groups. The slant of the quarry floor shows that the rock layers angle deep into the earth. Geologic pressures created the pipestone and quartzite layers over the past one billion years. Formed at the bottom of an ancient ocean, these layers of sediment were gradually compressed into stone and uplifted over the ages. The thick layers above and below the pipestone contained mostly silt and became quartzite, but the thin layer between was composed of fine clay, which is why the pipestone can be so easily worked. The quartzite and pipestone layers visible here, and another thick layer of quartzite below them, dip toward the east at a 5-10 degree angle. As pipestone quarrying continues, an ever increasing quantity of the upper quartzite must be removed.

Minnesota · United States