Rock Science
COAL-BLACK AS JET
BY STEVE VOYNICK
In Henry VI, William Shakespeare describes the Duke of Gloucester’s gown as “. . .
Black, forsooth: coal-black as jet,” a fitting simile for a pure, saturated black color.
Lexicologists suggest that our modern term “jet-black” stems directly from Shakespeare’s usage of the word “jet.” Not only is jet’s color, as Shakespeare noted, “coal-black,” jet is itself a form of coal.
A FORM OF COAL
Coal is technically a rock, a combustible material formed by the decomposition and destructive distillation of biomass material in an oxygen-free environment. Coalification, the process of coal formation, begins when layers of plant material become buried and compressed under new forest growth and sediments. Elevated temperatures and pressures then alter these organic remains, driving off water and volatile compounds and concentrating the carbon in the remaining material.
Coal consists primarily of carbon, together with some oxygen and hydrogen, and smaller amounts of sulfur, iron, nitrogen and other elements. Variations in burial time, heat and pressure produce four basic commercial grades of coal: peat, lignite, bituminous (including subbituminous) and anthracite.