Argillite is primarily composed of clay or silt particles, but may contain other constituents as well. When iron is present, the rock is commonly referred to as a ferruginous argillite. This type of argillite may be found in various locales, such as Missoula, Montana and Killarney Park in Ontario, Canada. A siliceous kind of argillite, on the other hand, is commonly known as zebra rock due to the alternating red and cream-colored bands it exhibits. An unusual sight to behold, occurrences of zebra rock argillite are only known in Western Australia.