Once upon a time, when I was just getting interested in crystals and gemstones, there was a large amethyst geode in the rock-shop window that used to taunt me with its enormous price-tag, far beyond my limited budget, and with the sheer beauty of the shiny, deep purple crystals in its interior, hidden by the forces of nature in a dark exterior as dull and unappealing as the fossilized habit of a mediaeval monk.