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Digital Subscriptions > Rock&Gem Magazine > April 2019 > PIPESTONE:The Sacred ‘Peace Pipe’

PIPESTONE:The Sacred ‘Peace Pipe’

The Rich History and Lore of Minnesota Argillite

Despite its mundane petrological classification as a mudstone, pipestone has a lot going for it. Its great workability, exceedingly fine grain, and attractive reddish-brown colors make it a fine carving medium.

More importantly, pipestone, also known as argillite and catlinite, has an extraordinarily rich history and great cultural significance. Sacred to many Native Americans, it is a symbol of tribal traditions and religions. And pipestone, also celebrated in Anglo-American art and literature, is the raison d’être of the National Park Service’s Pipestone National Monument in Pipestone, Minnesota.

Technically, pipestone is argillite, a mudstone that has undergone varying degrees of metamorphic alteration. As a lithified mud or ooze, it consists primarily of microscopic silt particles roughly 0.0025 inches (0.06 millimeters) in size and even smaller clay particles only 0.0008 inches (0.002 millimeters) in size. These particles are mainly those of sericite, a group of fine-grained, micaceous clay minerals derived from the weathering of orthoclase and plagioclase feldspars. These minerals specifically include pyrophyllite and kaolinite (both basic aluminum silicates), diaspore (basic aluminum oxide), and muscovite (basic potassium aluminum silicate).

Because it is devoid of quartz, pipestone has an approximate hardness of only Mohs 2.5 and can be scratched with a fingernail. With a specific gravity of 2.65, it is as dense as quartz. Pipestone occurs in uniform masses with occasional bedding planes. Its colors are sometimes slightly mottled and range from gray, black, and green to reddish and reddish-brown. The latter two hues are caused by tiny particles of hematite, or iron oxide, and are the classic and most prized pipestone colors.

Pipestone occurs at several North American localities in varying grades and colors. Its premier and most storied sources are the small quarries near the aptly named town of Pipestone, the seat of Pipestone County, located in the far southwestern corner of Minnesota near the South Dakota line.

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Rock & Gem April 2019, WorkShops in the Wild : Lifelong Learning at Wildacres, Emergence of Flourescence, Bladed Barite : In the East Potrillo Mountains, And More....