As all meteorite iron is nickel rich this indicated a meteoritic origin. Hadean Jack Hills zircon has a wide range of oxygen fraction comparing to meteoritic zircons. One of the fragments was made of bloomery iron rather than meteoritic iron. Crater lakes can be meteoritic or of the caldera variety. The meteoritic hypothesis is viewed by geologists as doubtful. Besides meteoritic iron, Thule people of Greenland have used native iron from the Disko region. The oldest known iron artifacts are nine small beads hammered from meteoritic iron. Small graphitic crystals in meteoritic iron are called cliftonite. Its meteoritic origins were first conclusively demonstrated by Ivan Reinvald in 1928, 1933 and 1937. They can be produced by impact events such as an explosion or meteoritic impacts. Most troilite on Earth is of meteoritic origin. Like other carbonados it is believed to be of meteoritic origin. In 2013 evidence that it is meteoritic in origin was presented. The glass is about 90% local sand and 10% meteoritic iron and nickel. Singing bowls are also sometimes said to incorporate meteoritic iron.