Gemology: H is for...
We take another journey into the realm of gemology with gemstones beginning with H. Take a look at the colourful world of Hackmanite, Harlequin Opal, Hawk's Eye, Heliodor, Heliotrope, Hematite, Hemimorphite, Hessonite, Honey Opal, Howlite, Hyacinth, Hyalite, and Hydrogrossular Garnet.
Hackmanite is pink sodalite mineral first noted in Greenland in 1896, but not found in gemstone quality until a discovery in Quebec in 1991. It's an unusual gemstone in that it's bright pink to violet until exposed to sunlight, whereupon the colour fades completely! But the colour comes back if the gem is placed in darkness for a short while. This process can be repeated endlessly but is destroyed if the gemstone is exposed to prolonged heat. There is also a variant of Hackmanite found in Afghanistan and Myanmar that has a reversed effect, being almost colourless in darkness but flaring into bright pink-purples when exposed to sunlight. These changes of colour are known as tenebrescence and are the rarest form of colour change in minerology.
Image Attribution: By DonGuennie|G-Empire The World Of Gems (Own work http://www.g-empire.de) [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons
Harlequin Opal Harlequin is a very rare variant of opal in which the colours are arranged in neat rectangles or diamond shapes, much like a harlequin costume.