can be calculated using the following equation: where: Natural freshwater diatomaceous earth is preferred by many researchers over chromic oxide, which has been widely used for the same purpose, the latter being a known carcinogen and, therefore, a potential hazard to research personnel. Construction Spent diatomaceous earth from the brewing process can be added to ceramic mass for the production of red bricks with higher open porosity. Diatomaceous earth is considered a very prominent inorganic non-metallic material that can be used for the production of various ceramics, including production of porous ceramics under low temperature hydrothermal technology. Specific varieties Tripolite is the variety found in Tripoli, Libya. Bann clay is the variety found in the Lower Bann valley in Northern Ireland. Moler (mo-clay) is the variety found in northwestern Denmark, especially on the islands of Fur and Mors. Freshwater-derived food grade diatomaceous earth is the type used in United States agriculture for grain storage, as feed supplement, and as an insecticide. It is produced uncalcinated, has a very fine particle size, and is very low in crystal silica (<2%). Salt-water-derived pool / beer / wine filter grade is not suitable for human consumption or effective as an insecticide. Usually calcinated before being sold to remove impurities and undesirable volatile contents, it is composed of larger particles than the freshwater version and has a high crystalline silica content (>60%). Microbial degradation Certain species of bacteria in oceans and lakes can accelerate the rate of dissolution of silica in dead and living diatoms by using hydrolytic enzymes to break down the organic algal material. Climatologic importance The Earth's climate is affected by dust in the atmosphere, so locating major sources of atmospheric dust is important for climatology. Recent research indicates that surface deposits of diatomaceous earth play an important role. Research shows that significant dust comes from the Bodélé Depression in Chad, where storms push diatomite gravel over dunes, generating dust by abrasion. Safety considerations Inhalation of crystalline silica is harmful to the lungs, causing silicosis. Amorphous silica is considered to have low toxicity, but prolonged inhalation causes changes to the lungs. Diatomaceous earth is mostly amorphous silica but contains some crystalline silica, especially in the saltwater forms. In a 1978 study of workers, those exposed to natural diatomaceous earth for over five years had no significant lung changes while 40% of those exposed to the calcined form had developed pneumoconiosis. Today's