What about Corundum that's not Suitable for Jewelry?
Corundum that is not of gem quality is most often found in metamorphic or igneous rock formations and is most often used to make emery, abrasive grinding products, due to its hardness. Most gem quality corundum is found in alluvial gravel deposits (scraped and left by glaciers) due to the fact that not only is it hard enough to withstand all of that abuse, but also because corundum is very heavy (making it easy to pan for), such as the locations where I search in Mitchell County, North Carolina. Corundum can be found in North America (Montana and North Carolina being the best-known), as well as in Russia, Australia, Thailand and Africa, and a lot of gem quality material comes from mines in India.
Isn't it odd that these two well known gemstones, whose only difference is their color, are actually the same mineral? Perhaps the separation occurred during corundum's long history of being used as personal ornaments, jewelry, statues and icons, often chosen by color for a variety of reasons, some of which follow: