A new month, a new stone, and again we have a well known ‘variety’. Aquamarine is known to be the traditional birthstone for March and is light blue-green to cyan variety of the mineral beryl. Beryl got its name from the beryllium within its crystal composition and today is still a major source of beryllium metal. Now that doesn’t mean we are crushing up beautiful crystals of aquamarine for beryllium. In fact only a small percentage of gemstone minerals are gemstone grade, the majority looks like stones you find on the beach. Beryl is also a tough stone with a Mohs hardness of 7.5-8, making it harder than amethyst and garnet.
To get a little nerdy and continue the theme of the other blog posts. Aquamarine is identified as:
- Hexagon Crystal System, not to be confused with crystal habit. (Note, habit is how the mineral crystallizes)
- Silicate Composition,
- Cyclosilicate Sub-class
- Silicate Family
- Mineral = Beryl – Be3Al2Si6O18
- Variety = Aquamarine.
Other varieties of beryl aside from aquamarine that you may know well are: emeralds (deep vivid green), morganite (light pink/peach), and heliodor (golden yellow). However, there are other kinds as well such as goshenite (colourless), red beryl (deep red/crimson), green beryl (light lime to mint green) and mixixe (deep blue colour but fades to brown in daylight due to UV).
All of these varieties, aside from goshenite, get their colour from additive elements locked into the crystal lattice or structure during crystallization. Aquamarine, (aqua marina) latin for “sea water”, which is a fitting name if you ask me, gets it colour from small traces of iron in the crystal structure. For those that remember their chemistry class on valence electrons, in deeper detail the blue tones come from Fe2+ while the green tones come from trace amounts of Fe3+. Hold on, but iron also colours amethyst purple and garnets red? That’s true too, but it all comes down to chemistry and light, how the iron electrons interact with the other elements in the crystal. This won’t be the last of iron as we get into detail about the other birthstones.
How can you tell if your aquamarine is an actual aquamarine? Well for starters the supply and demand of aquamarine doesn’t motivate the darker side of the trade unlike the regal rubys, sapphire, diamonds, and aquamarines sibling, emerald. However, there are those that will try to sell “aquamarine” coloured cubic zirconia and synthetic quartz. One quick method to tell these apart is to look for inclusions within the crystal. Cubic zirconia and synthetic quartz is virtually flawless and will look the same from all angels. Aquamarine is known for its flawless crystals but if you have a loupe (small 10x power microscopic lense used by many in the rock and gem trade) you can see smaller inclusions, such as, silk-like threads or small clear blebs or even other minerals within the aquamarine. As for the colour, beryl is anisotriopic, meaning light behaves differently depending on the direction it travels through the crystal. This appears weakly in aquamarine as it will look colourless to blue depending on how you look at it. A polarized lens can help you see this better. Meanwhile CZ looks the same from any angle. The best option is getting a certified gemmologist to look at the stone as they can give you a definite answer, they are professionals after all.
Now for some interesting facts about aquamarine for you. One thing many people don’t know is the colour can be heat treated. In North American markets we tend to desire the bluer variety over the more seafoam green colour. Through heat treatment, the green is lost and the blue enhanced. This kind of treatment is almost undetectable even to gemmologists and thus we actually assume all blue aquamarines are heat treated (especially the really vivid ones) unless certified 100% not treated. Even then, buyers beware. Due to its sea-like colour, many ancients associated aquamarine with the sea and sailors of ancient Rome believed it helped protect them during voyages. The largest aquamarine ever extracted was uncovered in Marambaia, Minas Gerais, Brazil, in 1910 and weighed over 110 kg (243 lb), and its dimensions were 48.5 cm (19 in) long and 42 cm (161⁄2 in) in diameter. That oughta bring a bunch of luck for the sailor who has that one on board.
Stay tuned for next month as we discuss diamonds.