Physical Properties: Magnesium carbonate typically appears as a white granular powder, white friable lumps, or a loose white powder; it is odorless and tasteless. It has a relative density of approximately 3.037, is slightly soluble in cold water, insoluble in ethanol, and dissolves in dilute acids with effervescence. It is hygroscopic and oil-absorbent and is stable in air; however, it decomposes into magnesium oxide and carbon dioxide when heated to 700°C. It decomposes upon contact with dilute acids, releasing carbon dioxide, and reacts readily with water when heated to form magnesium hydroxide.
Chemical Properties: Magnesium carbonate reacts with acids to produce the corresponding magnesium salts and carbon dioxide gas; for example, it reacts with hydrochloric acid to form magnesium chloride, water, and carbon dioxide, and with sulfuric acid to form magnesium sulfate, water, and carbon dioxide. It also reacts with ammonium salt solutions and is readily soluble in strongly alkaline solutions.
It exists as basic hydrated magnesium carbonate or normal hydrated magnesium carbonate. Depending on crystallization conditions, the product is classified as either "light" or "heavy," with the light variety being the most common. At room temperature, it exists as a trihydrate. The light variety appears as white friable lumps or a loose white powder; it is odorless and stable in air. When heated to 700°C, it releases carbon dioxide and forms magnesium oxide. It is virtually insoluble in water but imparts a slightly alkaline reaction to the water. It is insoluble in ethanol but dissolves in dilute acids with effervescence.