Physical Properties
Food-grade diatomaceous earth is a soft, chalky, highly porous powder. It is insoluble in water, and has a melting point of 1,710 degrees Celsius, a boiling point of approximately 2,200 degrees Celsius and a density of 2.3 g/cm^3. It is gently abrasive, which makes it useful in toothpastes, metal polishes and other cleaning compounds.
Chemical Properties
Diatomaceous earth is essentially chemically inert. It does not react with most chemicals, and has a very low toxicity. This makes it safe to use as a bulking ingredient; pills and foods often include silicon dioxide or silica in their list of ingredients. It also has a high absorption rate, and can soak up more than its own weight in liquid while behaving like a dry powder.
Insecticidal Properties
Diatomaceous earth's abrasive and desiccant properties make it a potent natural insecticide. When insects come in contact with diatomaceous earth, its microscopic sharp edges lacerate them, draining their body fluids and killing them. It also dehydrates fungi, molds and spores in the garden, without harming plants or seeds.
Other Uses
Diatomaceous earth's air-filled structure makes it a moderately good insulator, since dead air space does not transmit heat. It has a thermal conductivity rating of 0.07 W/(m·K), or watts per meter kelvin, which is about the same as paper. Its absorptive capacity led the Swedish inventor Alfred Nobel to combine it with liquid nitroglycerin to make a solid, stable and malleable explosive called dynamite.