Aquamarine – March Birthstone

It’s time to dig deep into the science of the gemstone aquamarine and its mineral family today. This post will definitely be more science-y than my last post about birthstones which was about the amethyst, which can be considered a fairly “simple” gemstone.

I’m so excited to teach you all about this pastel blue dream of a gemstone and its mineral family so let’s just dive right on in shall we!

The aqua stone

The name aquamarine came to surface in the early 18^th century and is derived from the latin aqua marina which literally means ‘seawater’ and is of course a reference to its sea-blue colour. The gem has been a popular talisman to wear by seafarers for centuries since it was said to protect them during their travels by sea, as well as from drowning and seasickness. I might test this theory for my next time on the sea since I get seasick very easily..

 

Delicate, minimal and everyday jewellery featuring aquamarines. Made by yours truly.

 

 

The beryl family

The gemstone aquamarine is one of 8 varieties within the popular beryl family, all of which are characterized by their specific colour, and I’m sure you have heard about most of them. Beryl is a mineral which is most commonly found in granitic* pegmatites** where it has been found in epic sizes several meters tall!

 

Left: giant beryl crystals found in 1928 at the Bumpus Quarry, Albany. Right: beryl crystal in quartz.

 

* The word ‘granitic’ is referred to its mineral composition, which in this case is composed of quartz, feldspar and mica, minerals that you would find in a common granite.

** Pegmatites are rock formations that form in the later stages of a granitic magma chamber’s crystallisation. Pegmatites are characterized by their larger crystal sizes which can be 2.5cm to several meters in size. The bigger crystal sizes within these rock formations is due to a very slow cooling process, which allows the crystals to grow BIG.

 

Top left: granite. Top right: pegmatite. Notice the hammer in the lower left corner for scale. Lower left: where pegmatites form relative to the granitic magma it originated from. Lower right: pegmatite intrusion covering a massive cliff face.

 

Beryl is a beryllium aluminium cyclosilicate mineral with the chemical formula Be₃Al₂(SiO₃)₆. To explain, cyclosilicate or ring silicate refer to the arrangement of the Si (silica) and O (oxygen) atoms within the crystal structure. When it comes to the beryl, these atoms are arranged in such a way that it gives the beryl crystal its characteristic hexagonal shape.

 

Left: the atomic arrangement in a cyclosilicate mineral. Blue spheres are oxygen (O) and red spheres are silica (Si). Right: the hexagonal shape of the beryl, aquamarine variety.

 

Beryl varieties

Pure beryl is colourless, but it is frequently tinted by impurities; possible colours are blue, green, yellow, pink and red. All of these colours represent one or two specific beryl varieties.

• Blue – aquamarine and maxixe
• Green – emerald
• Yellow – golden beryl and heliodor
• Pink – morganite
• Red – red beryl or bixbite
• White / colourless – goshenite

Aquamarine

Aquamarine is the blue or cyan variety of beryl and can be found at most localities which yield ordinary beryl. The deep blue version of aquamarine is called maxixe which is most commonly found in Madagascar. The pale blue colour of aquamarine is attributed to Fe²⁺ ions, whereas the deep blue colour of maxixe comes from when both Fe²⁺ and Fe³⁺ is present.

Advanced: The difference between the two Fe-ions is their oxidation state, which describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. If an ion looses an electron to another element in the compound it gets a higher positive charge, if it gains an electron it gets a lower positive charge. Conceptually, the oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic.

The largest gemstone quality aquamarine ever mined was found in Minas Gerais, Brazil, in 1910. It weighed over 110 kg and its dimensions were 48.5 cm long and 42 cm in diameter.

 

Aquamarine specimens. Left and right ones are from my own private collection.

 

Emerald

Emerald is, as most of you already know, the green variety of beryl. But spoilers, emerald is the birthstone of May which means it will have its very own blog post.

Golden beryl and heliodor

Golden beryl can vary in colour from pale yellow to a brilliant gold, with the colour being attributed to Fe³⁺ ions. The term “golden beryl” is sometimes synonymous with heliodor, but golden beryl refers to pure yellow or golden yellow shades, while heliodor refers to more greenish-yellow shades.

 

Left: heliodor and golden beryl beads in my own inventory. Note the slight difference in shade. Top right: heliodor. Lower right: golden beryl. 

 

 

Morganite

Morganite is a rather rare gem. It is the pink variety of beryl and is also known as “pink beryl”, “rose beryl”, “pink emerald” and “cesian beryl”. It can vary in shades from light pink to rose. Orange/yellow varieties of morganite can also be found and colour banding is quite common. The pink colour is attributed to Mn²⁺ ions.

Pink beryl of fine colour and good sizes was first discovered on an island on the coast of Madagascar in 1910. In 1989, one of the largest gem morganite specimens ever uncovered was found in Maine, US. The crystal was 23 cm (9 in) long and about 30 cm (12 in) across, and weighed just over 23 kg (50 pounds).

 

Left: morganite with intergrown tourmaline. Right: morganite beads from my own inventory.

 

Red beryl

Red beryl, or bixbite, is the very rare red variety of beryl. As with morganite, red beryl gets its colouration from Mn, but from Mn³⁺ ions and not Mn²⁺ ions as in the case of morganite. As of to date, red beryl has only been found within the United States. The greatest concentration of gem-grade red beryl comes from the Ruby-Violet Claim in the Wah Wah Mountains in mid-western Utah. Unlike most other beryl varities, red beryl is usually highly included.

While gem beryls are ordinarily found in pegmatites, red beryl occurs in topaz-bearing rhyolites. Rhyolite is a volcanic rock and can be considered as the extrusive equivalent to the plutonic granite rock. Red beryl is formed by crystallising under low pressure and high temperature along fractures or within near-surface cavities of the rhyolite.

 

Red beryl. Note the high amount of inclusions. Perfectly imperfect in my opinion!

 

Goshenite

Goshenite is the colourless beryl variety and its name originates from Goshen, Massachusetts, where it was first discovered. The gem value of goshenite is relatively low and it can be found to some extent in almost all beryl localities.

Since pure beryl is colourless, one would assume that goshenite is the purest of them all. However, this assumption may not always be true as there are several elements that can act as colour inhibitors in beryl.

 

Goshenite specimens. The one on the right features an intergrown tourmaline crystal and colour impurities.

 

That’s a wrap

I hope you found this post interesting, I at least had a lot of fun writing it and doing some research on this interesting and beautiful mineral family.

So, if you ever want to find your own aquamarines or any of the other beryl varieties, the first step is to find yourself some pegmatite outcrops.

Happy hunting!

Linda