Baku, October 29 (AZERTAC). An auction of Fine Jewelry will feature a rare Heart-shaped, 98-carat natural Black Diamond. Cut from a piece of rough weighing 320 carats in the state of Bahia, Brazil, in 1951, the diamond is estimated to realize $70,000-$90,000. Unlike diamonds formed deep under the earths` surface in an environment of tremendous pressure and heat, black diamonds are uniquely found in surface alluvial deposits only in Brazil and the Central African Republic, and contain gases indicating their possible extra-terrestrial origins. It is not unusual to suffer significant weight loss during cutting black diamonds. They are porous, and difficult to cut and polish due to their lack of cleavage plane, requiring a time-consuming process to fashion the polycrystalline rough into faceted gemstones.