Lignum vitae is one of the most amazing natural wonders of the world.  The quotes below are from wikipedia and are verified in numerous places.  I am truly amazed by this wood.

    "Lignum vitae is hard and durable, and is also the densest wood traded (density: 1.23 g/cm3 [3]); it will easily sink in water. On the Janka Scale of Hardness, which measures hardness of woods, lignum vitae ranks highest of the trade woods, with a Janka hardness of 4500 lbf (compared with African Blackwood at 2940 lbf, Hickory at 1820 lbf, red oak at 1290 lbf, Yellow Pine at 690 lbf, and Balsa at 325 lbf)

  The aft main shaft strut bearings for USS Nautilus (SSN-571), the world's first nuclear-powered submarine, were composed of this wood. Also, the bearings in the original 1920s turbines of the Conowingo hydroelectric plant on the lower Susquehanna River were made from lignum vitae. The shaft bearings on the horizontal turbines at the Pointe du Bois generating station in Manitoba are made from lignum vitae. Other hydroelectric plant turbine bearings, many of them still in service, were fabricated with lignum vitae and are too numerous to list here."