Chert also occurs in diatomaceous deposits and is known as diatomaceous chert. Other source materials include chalcedony, quartzite, andesite, sandstone, chert, and shale. Some of the chert clasts actually contained fossils. The rock types include marble, chert, limestone, shale, and sandstone. Banded iron formations (BIF) are sedimentary rocks of layered iron oxide and iron-poor chert. They sometimes grade locally into chert or dolomite. Lake Magadi is also well known for its extensive deposits of siliceous chert. It is found along with smaller amounts of chert, and black schist. The quarries are cut in beds of white-grey limestone separated by chert beds. Predominant rock types include shale and graywacke, with greenstone, tuff and chert. They made spear points of jasper, quartz, shale, or black chert. Veins of felsic, chert and ultramafic material intrude the belt. It is usually made from flint or chert. They created stone tools made out of chert by chipping, knapping and flaking. Ancient microfossils have been found in the banded iron formations of the Gunflint Chert.