other rock types but lacustrine diatomites are almost always associated with volcanic rock. Diatomaceous chert consists of diatomite that has been cemented with silica. Diatoms are able to extract silica from water that is less than 1% saturated in amorphous silica (saturation index (SI): -2). Their frustules remain undissolved because they are surrounded by an organic matrix. Clay minerals may also precipitate on the frustules and protect them from dissolution in sea water. When the diatom dies, the frustule is stripped of its organic layer and exposed to sea water. As a result, only 1% to 10% of frustules survive long enough to be buried under sediments and some of this is dissolved within the sediments. Only an estimated 0.05% to 0.15% of the original amount of silica produced by diatoms is preserved in the sedimentary record. Discovery In 1836 or 1837, German peasant Peter Kasten discovered diatomaceous earth (German: Kieselgur) when sinking a well on the northern slopes of the Haußelberg hill, in the Lüneburg Heath in North Germany. The extraction site on the Lüneburg Heath was 1863–1994 Neuohe, while the storage sites were: The deposits are up to thick and are all of freshwater diatomaceous earth. Until World War I, almost the entire worldwide production of diatomaceous earth was from this region. Other deposits In Poland diatomaceous earth deposits are found in Jawornik, and are composed mostly of diatomaceous skeletons (frustules) In Germany, diatomaceous earth was also extracted at Altenschlirf on the Vogelsberg (Upper Hesse) and at Klieken (Saxony-Anhalt). There is a layer of diatomaceous earth more than thick in the nature reserve of Soos in the Czech Republic. Deposits on the Isle of Skye, off the west coast of Scotland, were mined until 1960. In Colorado and in Clark County, Nevada, United States, there are deposits that are up to several hundred meters thick in places. Marine deposits have been worked in the Sisquoc Formation in Santa Barbara County, California near Lompoc and along the Southern California coast. This is the world's largest deposit of diatomite. Additional marine deposits have been worked in Maryland, Virginia, Algeria and the MoClay of Denmark. Freshwater lake deposits occur in Nevada, Oregon, Washington and California. Lake deposits also occur in interglacial lakes in the eastern United States, in Canada and in Europe in Germany, France, Denmark and the Czech Republic. The worldwide association of diatomite deposits and volcanic deposits suggests that