Sioux quartzite formed about 1.2 billion years ago when intense heat and pressure transformed pure quartz sandstone from an ancient sea into quartzite. Glaciers later left sediment in some places and exposed rock and outcroppings in others, and the quartzite bed at East Sioux Falls extends from southwest Minnesota into Minnehaha County, South Dakota. A federal geological survey in 1889 found the quartzite beds to be between 3,000 and 4,000 feet deep, with colors ranging from light pinks to deep purples, and in some places veins of pipestone are embedded in the quartzite. Pipestone, used by Native Americans for pipes, is easily carved, while quartzite is one of the hardest stones in the world, composed of 96 percent silica and 4 percent iron. Also known by names including jasper and granite, quartzite was identified by John F. Merriam of Springfield, Massachusetts, as distinct from granite; he found it harder than granite, more resistant to heat and acid, and especially valuable as a building stone because of its strength, beauty, and rich colors. Quarrying quartzite in the early days was labor-intensive work that relied first on quarrymen, who pried large slabs loose from exposed outcroppings or used lines of drilled holes packed with explosives to blast rock from the bed, and then on skilled stone cutters, who split the stone with plugs and feathers and shaped it with hammers and chisels into paving blocks and architectural elements. Finished stone was loaded onto railroad cars and shipped throughout the United States.