Encyclopaedia

North Atlantic Ocean off North America in which more than 50 ships and 20 airplanes are said to have mysteriously disappeared. The area, whose boundaries are not universally agreed upon, has a vaguely triangular shape marked by the southern U.S. coast, Bermuda, and the Greater Antilles. Reports of unexplained occurrences in the region date to the mid-19th century. Some ships were discovered completely abandoned for no apparent reason; others transmitted no distress signals and were never seen or heard from again. Aircraft have been reported and then vanished, and rescue missions are said to have vanished when flying in the area. However, wreckage has not been found, and some of the theories advanced to explain the repeated mysteries have been fanciful. Scientific searches have revealed nothing to substantiate the storied peril of the r...

Diamond-making techniques have been embraced by Earth scientists in their efforts to simulate conditions in the Earth's deep interior. Of special significance were the high-pressure syntheses of two new forms of silicates. In 1960 Sergei Stishov, while at the Institute of High-Pressure Physics in Moscow, subjected ordinary beach sand (composed of the mineral quartz SiO 2 ) to more than 8 GPa of pressure and high temperatures. The form of silica that he produced was approximately 62 percent denser than quartz and was the first known high-pressure compound to contain silicon in six-coordination rather than the four-coordination found in virtually all crustal minerals. The natural occurrence of this new synthetic material was confirmed within a few weeks by careful examination of shocked material from Meteor Crater, Ariz., U.S. The mineral was named stishovite. In 1974 a second high-pressure discovery revolut...