Catlinite (also called pipestone or pipeclay) is a type of argillite (metamorphosed mudstone), usually brownish-red in color, which occurs in a matrix of Sioux quartzite. Because it is fine-grained and easily-worked, it is prized by Native Americans for use in making sacred pipes commonly referred to as peace pipes, or calumets (Fr: "hollow reed"). Pipestone quarries are located and preserved in Pipestone National Monument outside of Pipestone, Minnesota, in Minnehaha County, South Dakota, and at the Pipestone River in Manitoba, Canada.
The Canadian quarry is no longer used, although there are quarries in Canada where prized black stone is gleaned. The Ojibwa use the black stone for their sacred pipes. The red catlinite from the Pipestone quarries is the second softest rock in the world, and it lays under Sioux quartzite, the second hardest rock in the world. Only hand tools are used to reach the catlinite so it takes a long time to get to it. Only enrolled Native Americans are allowed to quarry for the stone at the Pipestone National Monument, and so it is protected from over-mining due to this. The stone in the photo shown to the right is not the correct color or consistency for making pipes, it is too brittle. Catlinite is buttery smooth, and soft with no quartzite in it so it is easy to carve and cut with a regular hacksaw or even a knife, it comes out of the ground a pinkish color often with a cream layer protecting it from the hard quartzite.
The term Catlinite came into use after the American painter George Catlin visited the quarries in Minnesota in 1835; but it was Philander Prescott who first wrote about the rock in 1832, noting that evidence indicated that American Indians had been using the quarries since at least as far back as 1637.