Coal the heat and pressure of deep burial causes the loss of water, methane and carbon dioxide and an increase in the proportion of carbon. Thus first lignite (also called "brown coal"), then sub-bituminous coal, bituminous coal, and lastly anthracite (also called "hard coal" or "black coal") may be formed. The wide, shallow seas of the Carboniferous Period provided ideal conditions for coal formation, although coal is known from most geological periods. The exception is the coal gap in the Permian–Triassic extinction event, where coal is rare. Coal is known from Precambrian strata, which predate land plants—this coal is presumed to
Portrait of a Man with a Blue Chaperon a fur lined brown jacket over a black undervest. His headdress, a chaperon, contains two wings which hang down over the man's shoulders and extend to his chest. The edges of the cloth are given a shredded look at the edges of their trains. The hood is brightly and dramatically coloured using pigment extracted from the expensive lapis lazuli gemstone to give it its bright, intense hue. The headdress is of a similar but less extravagant type to that seen in van Eyck's c. 1433 "Portrait of a Man", and worn by a figure in the distance in his c.