en shows that it is secondary, formed by replacement of calcium by magnesium in limestone. The preservation of the original limestone texture can range from almost perfectly preserved to completely destroyed. Under a microscope, dolomite rhombs are sometimes seen to replace oolites or skeletal particles of the original limestone. There is sometimes selective replacement of fossils, with the fossil remaining mostly calcite and the surrounding matrix composed of dolomite grains. Sometimes dolomite rhombs are seen cut across the fossil outline. However, some dolomite shows no textural indications that it was formed by replacement of limestone. Occurrence and origin See also: Dolomitization Dolomite is widespread in its occurrences, though not as common as limestone. It is typically found in association with limestone or evaporite beds and is often interbedded with limestone. There is no consistent trend in its abundance with age, but most dolomite appears to have formed at high stands of sea level. Little dolomite is found in Cenozoic beds (beds less than 65 million years old), which has been a time of generally low sea levels. Times of high sea level also tend to be times of a greenhouse Earth, and it is possible that greenhouse conditions are the trigger for dolomite formation. Many dolomites show clear textural indic