Gemology: A is for ...

Wow, there are so many gemstones out there! We all know the most common precious stones: Emerald, Ruby, Sapphire etc. but do you know any of these less well known semi-precious gems? Our pictorial guide will give you head start on gems beginning with A!

A Selection of Colourful Mineral Gemstones

A Selection of Colourful Mineral Gemstones

On this page you will find the wonderfully colourful world of Abalone, Achroite, Actinolite, Adamite, Afghanite, Agate, Ajoite, AkoyaPearl, Alexandrite, Albite,

Almandine, Amazonite, Amber, Amblygonite, Amethyst, Ammolite, Andalusite, Andesine-Labradorite, Apatite, Apophyllite, Aquamarine, Aventurine, Axinite, and Azurite. Abalone OK, starting with a bit of a cheat - this one isn't a gem! Abalone is a kind of sea snail and the lining of its shell – mother-of-pearl – is prized for jewellery decoration. You'll usually find it forming a layer or inlay for a coloured background as it's not suitable to be cut like a gem.

Inside an Abalone Shell Showing Mother-of-Pearl

Inside an Abalone Shell Showing Mother-of-Pearl


Achroite is a colourless variety of Tourmaline (we'll get to gems starting with T later!), also known as white tourmaline. In its purest form it's ideal for cutting into gems for jewellery.

Achroite Raw Crystal

Achroite Raw Crystal


Actinolite, also known as Actinolite Cat's Eye, is a rare pale yellowish green gemstone that looks best when cut cabochon (see our glossary for Cabochon definition). Cutting the gem with facets ruins it's milky opaqueness and the 'cat's eye' effect of its light refraction. The best deposits are in Canada but it's also found in Western Australia, Brazil and Madagascar.

Actinolite Raw and Polished Cabochon

Actinolite Raw and as a Polished Cabochon

(Image Attribution: Rob Lavinsky, – CC-BY-SA-3.0 [CC BY-SA 3.0 (], via Wikimedia Commons)

Adamite Adamite is a very rare mineral gemstone that's generally considered too soft for jewellery. It was first documented in 1866 by Frenchman Gilbert-Joseph Adam who discovered the mineral in Chili, This beautiful gem fluoresces a bright green under ultraviolet light, but is a yellow to yellow-green in natural light, and occasionally found in blue or violet colours. It's probably a good thing that Adamite is not really suitable for jewellery (though some gems have been set in jewellery before) because this mineral contains arsenic!

Adamite Fluorescing Bright Green

Raw Adamite Crystal showing the Beautiful Depth of Lime Green Colour (Picture Attribution: Rob Lavinsky, – CC-BY-SA-3.0 [CC BY-SA 3.0 (], via Wikimedia Commons)

Afghanite Relatively newly identified, Afghanite was first documented in 1968 having been discovered in northern Afghanistan, Afganite has a stunning bright blue colour that fluoresces brightly under ultraviolet light. Not all afghanite mined is clear and pure enough to be cut into gemstones so this remains a highly prized and collectible gem.

A Clear Bright Sapphire Blue Afghanite Crystal

A Clear Bright Sapphire Blue Afghanite Crystal (Rob Lavinsky, – CC-BY-SA-3.0 [CC BY-SA 3.0 (], via Wikimedia Commons)

Agate Agates are semi-precious gemstones naturally occurring in many colours, including blue, brown, yellow, black, green, white, and grey. They're formed in pockets left in (largely volcanic) rocks where tiny quartz crystals fill the gaps layer by layer. Layers may form in different colours, influenced by environmental pressures, meaning that every single agate is unique. In jewellery agates are generally cut en cabochon (refer to glossary for definition) to enhance their colour.

Beautiful Red and White Agate Still in Formation

Beautiful Red and White Agate still in the process of 'filling in' with microcrystalline quartz

(Photo Attribution: James St. John via Commons Media)

Ajoite Pronounced ah-hoe-ite, this gem was last found in Messina in 1991, but the mine flooded and has remained closed ever since. If you're lucky enough to own a peace of this mystical turquoise coloured mineral it's said that you will enjoy peace and harmony as it was highly prized by Papago Indians in Arizona - the only other place in the world it has been known to occur. As all known mines are closed or exhausted this is likely to remain a rare mineral for a very long time!

Raw Ajoite Mineral Deposit (Picture Attribution: Rob Lavinsky, – CC-BY-SA-3.0 [CC BY-SA 3.0 (], via Wikimedia Commons)

Akoya Pearl Akoya pearls are naturally produced when an irritant enters the shell of a saltwater oyster. The oyster builds a protective layer of nacre around the irritant, and it's this nacre that gives the pearl its lustrous glow. Once very expensive due to their near perfect roundness and the hit-and-miss process of oyster fishing, Akoya pearls are now cultured in special oyster farms where an irritant is artificially inserted into the mollusc.

Akoya Pearls with a Pinkish Hue

Akoya Pearls with a Pinkish Hue


Think diamonds are the most valuable gem in the world? Think again! Alexandrite, discovered in Russia in 1834, is so rare that it is possible the most expensive gem you could hope to buy. And with it's amazing colour changing ability, going from emerald green in daylight through to yellow and ruby red in candlelight, this chameleon gem is a most desirable gem indeed.

Alexandrite Gem Photographed in Different Lights

The Colour Change Seen When Alexandrite is Photographed in Different Lights (Picture Attribution: By User: at en.wikipedia [GFDL ( or CC-BY-SA-3.0 (], from Wikimedia Commons)

Albite Albite is a very common white crystalline mineral with a bluish tinge, often polished into gems called moonstones. It's found all over the world.

Albite in Crystalline Form

Albite in Crystalline Form

Almandine / Almandite Almandine, often incorrectly called almandite, is a fairly common form of garnet. Most garnets are a mixture of different garnet forms and those containing almandine are a darker, brownish red. Also known as the Ceylon Ruby.

Polished Almandine Garnet in Raw Mineral

Almandine Garnet, Ceylon Ruby (Picture Attribution: By Lech Darski (Own work) [CC BY-SA 3.0 (], via Wikimedia Commons)


Amazonite is a soft gem with a name that's something of a misnomer. It was named after the Amazon River, though it's unlikely that this is the original source of the gem with occurrences mainly in Europe and the United States, but it is similar to other stones found along the Amazon so the name is most likely a result of mistaken identity. Amazonite is a light greeny-blue colour (which is why it's also known as Amazon Jade) with a soft sheen to its surface. In jewellery use Amazonite is generally cut en Cabochon because its la