The largest deposits of diatomite in the world and in Russia are presented. The applications of diatomite and the properties of heat-insulating diatomaceous bricks are described.Diatomites, opokas, tripolis, spongiolites, and radiolarites form a group of sedimentary silica rock consisting predominantly of opal and cristobalite.The interest shown in the study of silicaceous rock is largely due to their useful properties. These rocks are minerals which possess a wide range of valuable properties. As a result, they are widely used in the national economy. Their characteristic features are the presence of amorphous active silicon dioxide on the one hand and a fine-porous structure, lightness, and low thermal conductivity on the other. These properties make these materials chemically highly active and make it possible to use them as sorbents, desiccants, catalysts, filtering and heat-insulating materials, and catalyst and filler carriers.Diatomites are light fine-porous rocks consisting mainly of extremely small opaline skeletons (or their fragments) of diatomic algae -diatoms. Diatomites are white, yellowish gray, light gray, and sometimes dark gray, and brownish gray. The dark and brown color of diatomites is due to the presence of organic impurities in them, including plant residues. The pores and the walls of pores of diatoms are often of nanosize, which justifies classifying them as nanomaterials. It is evident on photomicrographs (see Fig. 1) that each skeleton of diatoms in diatomite possesses a clearly ordered micro-and nanoporous structure [1]. This structure and the ordered size distribution of the pores give diatomite a low density and its high, compared with other similar materials, heat-insulating properties, on account of which they are used for thermal insulation of surfaces with temperature 900 -1000°C.The number of whole skeletons and their large fragments fluctuates over a wide range in diatomites: from less than 1 mm to more than 1 mm in diameter, the usual size being 10 -200 mm. The volume mass in a fragment, as a rule, does not exceed 1 and for the best varieties it equals 500 -700 and even 250 -300 kg/m 3 (Dzhradzorskoe and Masel'skoe deposits). The true density varies from 2 to 2.66 g/cm 3 , i.e., from glassy to the most common crystalline forms (b-quartz) [1].The character of the bedding and quality of diatomites are strongly associated with the conditions under which they were formed. The largest deposits of diatomites are found in marine sediments.Diatomites of marine origin, whose source of silica were products of erosion of the surrounding dry land, are most characteristic for epicontinental basins of the Paleogene. The main deposits of diatomites in the countries of the Commonwealth of Independent States have been found in deposits in Povolozh'e (Inzenskoe, Sengileevskoe, Atemarskoe, and others), Transurals, and Western Kazakhstan (Irbitskoe, Kamyshlovskoe, Potaninskoe, Kirgizskoe). Diatomites form beds in the form of layers up to 80 -100 m thick and large lenses in sandy and sand-opoka fo...
