Tablelands are often topped with argillite gravel and weathered quartzite, occasionally underlain by shale. Inuit artists sculpt with walrus ivory, caribou antlers, bones, soapstone, serpentinite, and argillite. They consist of metamorphosed graywacke, argillite, tuff, mafic igneous extrusive flows, and carbonate rock. All six of these formations are primarily composed of quartzite and argillite. These include turquoise, jet, argillite, steatite, red shale, freshwater clam shell, abalone, and spiny oyster. There is also Precambrian sedimentary argillite, dating back to 1.7 billion years ago. The deposits are hosted in shear zones in argillite of the Precambrian Belt Supergroup. Besides working in wood, Haida also work with argillite. Most carvers create a sculpture from a single piece of argillite wherever possible. An exhibit of artist Bill Reid's argillite carvings are also available for viewing. In the Skidegate dialect of the Haida language argillite is called "kwawhlhal". A Maori argillite quarry is located in the hills behind Nelson City. Instead of Kaufmann's three periods, Duff broke the history of argillite carving into four phases. This is when argillite carving began to incorporate Western elements and themes. The rock is originally external rocks brought by Kenting argillite.