Dolomite was first described in 1791 for exposures in what are now known as the Dolomite Alps of northern Italy . Dolomite was first described in 1791 as the rock by the French naturalist and geologist , DÃ odat Gratet de Dolomieu ( 1750 â `` 1801 ) for exposures in what are now known as the Dolomite Alps of northern Italy .