Dolomite

Dolomite is a calcium magnesium carbonate that forms one of the great puzzles in geology: the 'dolomite problem.' Despite being the most common magnesium-bearing sedimentary mineral, scientists have struggled for over 200 years to synthesize dolomite at surface temperatures in the laboratory. It forms easily in nature but refuses to crystallize under controlled conditions, suggesting that biological activity (microbial processes) may play a crucial role in its formation.

The Dolomite Mountains of northern Italy - one of the most spectacular mountain ranges in Europe - are composed primarily of ancient dolomite rock, and both the mountains and the mineral are named after French mineralogist Deodat de Dolomieu, who first described the mineral in 1791.

Dolomite crystals are famous for their distinctive curved 'saddle-shaped' or rhombohedral form. This curved crystal habit is almost unique to dolomite among common minerals and is one of its most recognizable features.

Dolomite is identified by its curved saddle-shaped crystal habit, hardness of 3.5-4, and slow reaction with dilute hydrochloric acid (it fizzes only in hot acid or when powdered, unlike calcite which fizzes readily in cold dilute acid). This slow acid reaction is the key distinction from calcite.

Distinguish from calcite (stronger acid reaction, different crystal forms), magnesite (similar chemistry but rarely well-crystallized), and quartz (much harder, no acid reaction). The curved crystal faces visible on well-formed specimens are essentially diagnostic.