Crushing different minerals creates different types of limes, two of which are agricultural lime (calcium carbonate) and magnesite (magnesium carbonate). Other limes, such as burnt lime (calcium oxide), hydrated lime (calcium hydroxide) and burnt magnesite (magnesium oxide), are the products of additional treatment, according to the NSW DPI.
High-quality agricultural lime contains crushed limestone with a 37- to 40-percent calcium consistency. Heating limestone drives out carbon dioxide and creates burnt lime. Treating burnt lime with water creates hydrated lime, which is used primarily in construction. Magnesite, consisting of crushed magnesium carbonate rock, contains virtually no calcium. When treating acidic soil already sufficient in calcium, some farmers use burnt magnesite. It contains about 50 percent magnesium, around twice as much as high quality magnesite, says the NSW DPI.