Gemology: G is for ...

Well this shouldn't take long; there really aren't that many and what we have are mostly variants of other minerals and gems! But if you're and you're going to read this don't worry about grabbing your coffee - it's really not going to have time to go cold! Welcome to the wonderful world of gahnite, gahnospinel, garnet and (yep, we're clutching at straws here!) glass.

Gahnite

Gahnite (also known as zinc spinel) is a rare variant of spinel distinguished by its high composition of zinc and the absence of magnesium. It's named after Johann Gottlieb Gahn who first described it 1807. Occurring in shades of green from yellowish to greenish-black, it can look good carved into jewels, especially in the peridot colours found in South America.

Image Attribution: Kay Günther / G-Empire The World of Gems / http://www.g-empire.de/ [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons)

Gahnospinel

Gahnospinel is a form of spinel that is rich in zinc, but midway between Gahnite and Spinel for its occurrence of magnesium - hence the name being a combination of both! Identified in 1937, Gahnospinel occurs in shades of blue, blue-green and purply-blue, with the rarest and most prized specimens being a clear blue gem. Because it occurs in the same Sri Lankan mines as sapphire it is often confused for the gem and can only be told apart by its light refraction.

Image Attribution: via gemstones-guide.com

Garnet

Most commonly known in its deep red form, 'Garnet' actually refers to a group of minerals occurring in many colours including purple, orange, yellow, green, brown, and – incredibly rarely – even blue! Garnets in shades other than red are generally given more descriptive names to distinguish them from red garnet, which is simply known as garnet. Garnet is a durable mineral that has been carved into jewels and worn for millennia. It is also the birthstone for January.

Image Attribution: By Michelle Jo (Own work) [Public domain], via Wikimedia Commons

Glass

Yes, glass is a naturally occurring gemstone!

We all know of man-made glass used in bottling and glazing, but glass also occurs naturally in areas where sand (silica) is heated to high temperatures before being cooled rapidly. Variants of glass include Obsidian (rapidly cooled lava flow), rare 26 million year old Libyan Desert Glass, and Darwin Glass from Mount Darwin in Tasmania. Natural glass doesn't have a great deal of brilliance but has still been carved into gems and used in jewellery and decorations. Man-made glass is cheap, easy to produce and colour, and frequently used in costume jewellery where it is often backed with a metal foil to increase brilliance. Lead is also often added to glass to increase its strength and light refraction and to give it more diamond like qualities, like the beautiful and famous Swarovski lead-glass crystals.

Image Attribution: By H. Raab (User:Vesta) (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC BY-SA 2.0 at (https://creativecommons.org/licenses/by-sa/2.0/at/deed.en)], via Wikimedia Commons.

Next week: "The Origin of Popular Wedding Traditions" Wedding season is in full swing so let's take a look at how and why some of the most popular wedding traditions started.

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