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

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.

Hawk's Eye

An opaque quartz gemstone with chatoyancy like Cat's Eye but in a bluish-grey colour. This mineral can be polished up beautifully for use in jewellery.

Helenite

Helenite is an artificial gemstone made from the volcanic ash of the Mount Saint Helens' Washington, USA, 1980 eruption. Workers doing reconstruction work following the eruption noted that their acetylene torches melted the ash into a green glass, and ensuing experiments showed heating the ash to 1480º Celcius would produce glass that could be faceted. Different dyes were added to the glass to produce artificial gemstones of green, red and blue, which are mounted into jewellery and sold to Mount St. Helens tourists. Being produced from volcanic ash, Helenite's closest relation would be obisidian, a naturally occurring volcanic glass.

Image Attribution: By Photo (c)2007 Derek Ramsey (Ram-Man) [GFDL 1.2 (http://www.gnu.org/licenses/old-licenses/fdl-1.2.html) or CC BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5)], from Wikimedia Commons

Heliodor Heliodor, from the Greek 'gift from the sun', is a form of Beryl that's yellowy-green in colour (also known as Golden Beryl). It's not often used in jewellery because it's slightly radioactive owing to trace elements of uranium, and lacks brilliance. It was discovered fairly recently alongside aquamarine crystals (also a form of beryl) in Namibia in 1910. Heliodor crystals can be very large with the largest – weighing in at 2054 carats – on display at the Smithsonian Institute in the US.

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

Heliotrope

Heliotrope is another name for Bloodstone; a red speckled dark green variety of chalcedony. Bloodstone is one of the birthstones for those born in March.

Image Attribution: By Ra'ike (see also: de:Benutzer:Ra'ike) (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Hematite / Haematite Hematite is a common form of iron oxide that can be polished up to create gemstones of a dark grey colour with a metallic sheen. When found in their natural form they are generally red owing to the rusting of the iron content, hence the 'haema' part of their name, meaning blood. Once polished and faceted they make a popular accent gem in many items of jewellery or decoration.

Image Attribution: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Hemimorphite

Hemimorphite is a rare gem quality form of zinc silicate occurring in tones of blue, green and white. The more translucent the sample, the more valuable, though it's a difficult gem to cut and polish. Usually it will be sold cut and polished en cabochon and is mainly sold to collectors, though it has been used in jewellery.

Image Attribution: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Hessonite

Hessonite is a yellowy-gold variant of Grossular Garnet, also known as Cinnamon Stone. Pure grossular garnet is clear but certain impurities lead to coloured variants, of which Hessonite is one. Hessonite is suitable for jewellery use and makes a transparent faceted gemstone.

Image Attribution: gemstoneuniverse.com/choose-gem/buy-hessonite-gemstone-online-india.html

Honey Opal

Honey Opals, as the name suggests, are a translucent honey-brown colour. They're an unusual looking opal that look fantastic when polished en cabochon. Looking at this opal, you would probably never guess that that's what it is!

Image Attribution: http://www.minerals.net/gemstone/opal_gemstone.aspx

Howlite

Howlite is an opaque whitish mineral with grey veining that resembles some forms of marble. It's popular for jewellery when polished into beads or used as gem chips. It's a porous stone so is easily dyed to resemble turquoise and coral.

Image Attribution: By Reitawood (Own work) [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons

Hyacinth This is an ancient biblical term for what would now most likely be called orange topaz, however, references to the gemstone 'Hyacinth' could mean any orange-brown gemstone as means of mineral classification were not so clearly defined in those times. Hyacinth is also known as Jacinth.

Uncut Hyacinth Gemstone, Orange Topaz Crystall

Image Attribution: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Hyalite Hyalite is another variant of opal, this time a transparent light yellow or blue. It has a glass-like quality, and is often confused for glass when cut as a gemstone. Also known as water opal.

Image Attribution: By Xth-Floor (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Hydrogrossular Garnet Hydrogrossular Garnet is a form of garnet closely resembling jade; generally green but also available in white and pink. It can be mottled with dark inclusions and is usually opaque. It's popular in both jewellery and carved into ornamental pieces.