Sioux Quartzite

More than 1.75 billion years ago, through a slow process of erosion and waves,
when this area was covered by small streams, many layers of sand were laid down. The rocks very slowly changed because of heat, pressure, and silica cement that bonded the individual sand grains. Some of the rocks are marked with groves, striations, and chattermarks when glacial ice scraped across them.
During the Wisconsin glacier, which was over a mile thick, the sediment left by other glaciers was removed, and some of the beautiful Sioux Quartzite was exposed. The Quartzite was cross-cut by shallow-wind eroded groves, when
sustained high velocity winds blew, leaving behind a smooth polished surface. Composed of almost 100 percent quartz, it is very resistant to erosion.
The colors in the quartzite layers vary from almost white/pink to a deep red/purple. The color comes from iron compounds coating the sand grains that make up the Sioux Quartzite. Iron oxides increase with the deeper color. Most of our boulders are of a rose color, thus the name of our website, rosecoloredrocks.com.
Over thousands of years, the lichens on many of the beautiful boulders, break down rock into rich black soil.
This is a very dense rock, with it's hardness being next to that of a diamond.