A-Z of Gemstones: A

Posted on the 18th November 2016

A to Z of Gemstones: A: Alexandrite, Amber, Amethyst, Aquamarine

ALEXANDRITE

Alexandrite is a very unique gemstone that was first discovered in the Ural Mountains in 1830 and was named after Alexander II, the Czar who ruled the Russian empire at that time.

Alexandrite is one of the most valuable varieties of the Chrysoberyl species. It is praised for its’ unique colour-change phenomenon where they turn from bluish green in daylight equivalent to purplish red in incandescent light. They get their colour from trace elements of chromium.

Very rarely some Alexandrites combine two phenomena, colour-change and chatoyancy and they are called “cat’s-eye Alexandrite”.

Depending on the transparency of the stone, which can be either transparent or translucent, alexandrites are mostly cut into faceted gems and cabochons.

Alexandrites’ lustre is vitreous to sub-adamantine; it rates 8.5 on the Mohs scale and is therefore ideal for jewellery that is worn frequently.

The Ural Mountains have yielded the finest alexandrites but the amount mined was very limited and so it is very hard to find a true Russian alexandrite today. Nowadays most alexandrites come from Sri Lanka and Brazil.

Synthetic alexandrite is available on the market. They are usually unrealistically clean and they display a blue/green and a vivid purple colour. They have the same chemical properties to that of natural alexandrite but their value is significantly lower and so they should always be disclosed as synthetic stones.

Materials that are most commonly used to imitate alexandrite are: synthetic colour-change corundum, synthetic spinel and glass.

The “Smithsonian Alexandrite” is one of the largest faceted Alexandrite samples in the world. It weighs 64.08cts, it is a cushion-mixed cut stone and it was mined in Sri Lanka.

 

AMBER

Amber is a fossilized tree resin and one of the most desirable organic gemstones.

Amber can be yellow, orange, red, brown and very rarely green and blue. The most sought-after amber is the transparent red coloured variety.

Amber is transparent to opaque and is usually cut into beads, cabochons or carved into decorative objects.

Amber’s lustre is waxy; it rates 2-2.5 on the Mohs scale which makes it suitable for jewellery such as necklaces, brooches and earrings which do not undergo as much wear. 

As opposed to other stones, amber’s inclusions are acceptable if not preferable; some types of amazing amber inclusions are insects and animals that lived hundreds of millions years ago.

The main sources of amber are countries in the Baltic Sea such as: Denmark, Germany, Lithuania, Poland and Russia as well as the Dominican Republic.

A common treatment of amber is heating in rapeseed oil to improve its transparency and dyeing it to create a more appealing colour.

Laboratories have produced reconstructed amber made with small pieces of amber that are pushed together using heat or pressure.

Materials that are mostly used to imitate amber are: copal, Bakelite, epoxy, glass and polyester.

 

AMETHYST

The name Amethyst is derived from the Greek word “amethystos” that means intoxicated, referring to the belief that the wearers of the stones were protected from intoxication.

Amethyst is the purple variety of Quartz and it comes in every tone and hue ranging from reddish purple to violetish purple. These colours are caused by colour centres.

Depending on the transparency of the stone which can be anything between transparent to opaque, amethysts are cut into faceted gems, cabochons, beads or shaped into carvings. Very commonly they are left intact as geodes, natural specimens of crystals still attached to their host-rock, that become beautiful decorative ornaments. Normally, amethysts are free from inclusions but they usually have colour-zoning and a typical inclusion of the stone is what is known as “zebra stripes” or “soap scum” which refer to parallel liquid inclusions.

Amethyst’s lustre is vitreous; it rates 7 on the Mohs scale which makes it suitable for jewellery that has secure settings to protect the stone from wear.

The main sources where amethyst is found are: Zambia, Brazil, Uruguay and other areas of Africa and South America.

The most common treatment for amethyst is heating in order to enhance or create the desirable vibrant purple hues. Synthetic amethyst has been widely traded since 1970. It has the same chemical properties as natural amethyst and because natural amethyst usually does not demand very high prices, the synthetic value is very similar.

Nevertheless, synthetics should always be disclosed as such. Materials that are most commonly used to imitate amethyst are glass and plastic. The “Empress of Uruguay” is the largest amethyst geode in the world. It is over three meters tall, weighing two and a half tonnes and it resides in Australia.

Amethyst is the February birthstone. 

AQUAMARINE

Aquamarine derives from the Latin words “aqua marina” which mean water of the sea.

Aquamarine is the bright blue variety of beryl species. Its colour can be pale to dark blue or greenish blue which is caused by iron trace elements.

Depending on the transparency of the stone which can be anything between transparent to almost opaque, aquamarines are cut into faceted gems, cabochons, beads or carvings and occasionally rough crystals are left intact in their hosting rocks and sold as gorgeous rough specimens.

Usually, aquamarines look clean when seen with the naked eye. A typical inclusion of the stone is what is known as “rainfall” consisting of parallel growth tubes.

Aquamarine’s lustre is vitreous; it rates 7.5-8 on the Mohs scale which makes it suitable for jewellery that has secure settings to protect the stone from wear.

The main sources of aquamarine are: Brazil, Pakistan, Myanmar, Namibia, Mozambique, Zambia, Kenya, China and the U.S.A.

The largest cut aquamarine in the world is the “Dom Pedro”, a 10,636ct obelisk –shaped stone.  The stone was cut by the world famous gem artist Bern Munsteiner.

The most common treatment for aquamarines is heating in order to enhance their colour and remove the yellow component to create a purer and more valuable blue.

Synthetic aquamarines exist in the trade but they are not as common as other synthetic gemstones. They have the same chemical properties as natural aquamarines but their value is significantly lower so they should always be disclosed as synthetics.

Materials that are most commonly used to imitate aquamarine are: treated topaz, synthetic spinel and glass.

Aquamarine is the March birthstone.