to travel the distance. Since their original formation, the caverns have been decorated by the formation of flowstone, stalagmites, and stalactites. Two stalagmite samples from the Aladdin's Cave section of the Treak Cliff Cavern have been found, by means of radioactive dating, to date back 111,000 years, proving that the cave itself is much older. The formations in Treak Cliff are stained orange or red by iron, white by lead, and occasionally green or blue by copper. Some of the stalactites have been distorted by variations in the flow to form twisted structures known as helictites. Blue John Trace elements from buried sediments, percolating rain water, and trapped sea water meant inorganic ions were present within the porous rock, among them chlorine, fluorine, sulfate, calcium, barium, lead, zinc, and even uranium. Organic material from the decomposing bodies of marine animals in the sediments formed hydrocarbons, precursors of oil and gas. At high pressure, a hot mineralised fluid formed and was forced into fractures and other voids in the rock. From this fluid, catalysed by the hydrocarbons, compounds such as galena (lead sulfide, PbS), sphalerite (zinc sulfide, ZnS), baryte (barium sulfate, BaSO4), and fluorspar (calcium fluoride, CaF2) were precipitated as solid crystals. At Treak Cliff the mineralised fluid was particularly rich in fluorine and 99% of the deposited mineral is fluorspar (technically, fluorite is the pure crystal and fluorspar the industrial name for the impure substance as mined). The exploitable deposits of fluorspar are known as "rakes", "scrins", "flats", or "pipes" depending on the size and shape of the voids in which the crystals were deposited. At Treak Cliff and nearby Blue John Cavern, the fluorspar is uniquely banded, ranging from blue-black to white. The exact cause of the coloration is disputed, but it seems that the formation of Blue John requires a rare combination of porous limestone containing a little hydrocarbon, small traces of radioactive elements, an impervious layer to prevent the mineral fluids and hydrocarbons from escaping, a high concentration of fluorine ions, and variations in conditions during the crystallization process to form the banded colours. The rarity of this combination of conditions explains the scarcity of Blue John. Because of its attractive banding and its rarity, Blue John has commercial value and ornaments made from it are much sought after by collectors. Historically, as well as from Treak Cliff and Blue John Cavern, veins of the mineral were