The ABC’s of Gemstones

Here is the alphabet or ABC's of gemstones just because there's just so many and much to know.  So I'm going to break it down for you one letter at a time.  I'm taking this alphabet one day at a time so check back daily to get your ABC's in Gemstones!

A is for Amber, Agate & Ammolite

Amber is tree resin that has fossilized over time and sometimes contains inclusions of plant or animal material, if you’re lucky.  Amber occurs in a variety of colors as well as the usual orangy-yellow-brown colour that is associated with the color amber.  Amber can range from white to pale bright yellow to brown and deep brownish black.  Ancient Germans called amber 'bernstein', or 'burn stone' because they burned amber as incense.  Clear colourless amber was considered the best material for rosary beads as it is smooth and silky to the touch.  Common amber is cloudy and opaque, whereas more highly priced amber is transparent.

Agate is a chalcedony quartz that forms in a wide variety of colours and textures, often in concentric layers.  Agate is characterised by it’s microcrystalline structure and brightness of colour.  The different agate forms include carnelian agate (reddish hues), blue lace agate, plume agates, moss agate, Botswana agate, fire agate, crazy lace agate/Mexican agate and eye agate among other varieties.

Ammolite is a valuable opal-like organic gemstone, made of the fossilized shells of ammonites which were cephalopods, or squid-like creatures.  Ammonites lived in tropical seas until the end of the Mesozoic era which was also the end of the dinosaurs. The fossilized shells that make up ammolite are composed mainly of aragonite, the same mineral that makes up nacreous pearls.  Ammolite is found along the eastern Rocky Mountains of North America and is the official gemstone of Alberta since 2004.   The quality of gem ammolite is determined by the number of primary colours, the way the colours play and the brightness of colours (iridescence).  All spectral colours found in nature are contained in ammolite and each colour represents a different layer of the gem.   Every ammolite gem shows a unique display of colour.  Never easily nor often imitated, ammolite only resembles a few gemstones: labradorite and broad flash black opal. 

B is for Beryl

Beryl is a species of gemstones which contains several varieties based on colour.  Pure beryl is colorless, but it is frequently tinted by impurities; which creates the potential colors such as green, blue, yellow, red, and white.   Blue aquamarine, green emerald, pink or peach morganite, yellow helidor, white goshenite and the most rare red bixbite. All from the same species although the price of the varieties varies depending on mining locations and rarity.

Citrine is the birthstone of November and member of the huge quartz family. This is a great gemstone with a durable hardness of 7 on the Mohs scale and relatively resistant to scratches. In the world of gemstones there are few yellow gems; although diamond and sapphire are yellow their expense may inhibit a buyer. Citrine occurs in shades from lemon yellow to deep reddish brown. Amethyst and smoky quartzes can be heated to become yellow, this today is very common in the trade but can only be recognised by a trained specialist.

Chalcedony is a  cryptocrystalline form of silica, which has a waxy luster waxy luster, and may be semitransparent or translucent.  Chalcedony assumes a wide variety of colors, but the most common are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black.  Each colour is it's own variety. 

Agate is variety of chalcedony with multi-colored angular or curved banding. 
Aventurine is is a form of chalcedony, translucent and containing platy mineral inclusions that give a shimmering effect termed aventurescence.  
Carnelian is a clear-to-translucent reddish-brown variety of chalcedony; the hue may vary from a pale orange, to a deep nearly-black coloration.  
Chrysoprase is a intense green variety of chalcedony, colored by nickel oxide.
Heliotrope, also known as bloodstone, is a green form of chalcedony containing red iron oxide inclusions which resemble drops of blood.
Moss agate contains inclusions that resemble filaments providing the superficial appearance of moss or blue cheese. 
Onyx has black and white banding 
Sardonyx is a variant of onyx with brown, red, orange and white banding

Corundum is naturally clear, however it comes in in every colour due to colour inducing impurities; red is ruby and everything else is sapphire. The line between red ruby and pink sapphire is the saturation and tone of the hue and the amount of chromium contained in the stone that gives that gorgeous red colour. Ruby comes in the star variety and sapphire comes in black and blue star sapphire. Pink-orange sapphire is a unique and labeled padparadscha sapphire.

D is for Diamond

Often imitated never duplicated, diamond is the most desired of all gemstones with round brilliant cuts being most popular.  Diamonds are mined in Central and Southern Africa, Australia, Russia and Canada.  Commercial deposits are actively mined in the Northwest Territories of Canada.  Diamond price is dictated by the carat weight, clarity, colour, cut and finally the certificate of a diamond. Although diamonds are desirable for their lack of colour, fancy coloured diamonds are a unique choice coming in nearly every colour.  Small defects in the chemical composition, or impurities of about one per million of lattice atoms create colours such as blue (boron), yellow (nitrogen), brown, green (radiation exposure), purple, pink, orange or red.  Worldwide cutting centers are located in Belgium, United States, Israel and India.

We covered emerald with beryl but as the most expensive stone of the family, let's go more in depth.  Emerald contain a host of mineral inclusions and is a naturally fractured stone filled with fissures.  With emerald you should expect eye visible inclusions, to tell you it's natural, otherwise it might not be real.  Eye clean emeralds are extremely expensive and even more rare in large sizes.  When emeralds are extracted from the mine, they are traditionally soaked in resinous cedar oil to fill the fissures, fractures and improve the stone's clarity and colour.  This is commonly accepted practice with emeralds and much care must be taken by jewellers when setting these stones, not to apply heat, which will damage the emerald.  Over time the cedar oil does come out but stones can be re-oiled to restore their natural beauty.  

F is for Fluorite

Fluorite is dubbed "the most colorful mineral in the world"; the most common colors being purple, blue, green, yellow, or colourless. Much less common are pink, red, white, brown, black, and almost every shade in between. The colour of fluorite is decided by factors such as impurities, exposure to radiation, and size of the colour centers.  With only a hardness of four on the Mohs scale, fluorite is a fragile stone, less common than other coloured stones found in jewellery.  Fluorite often has multiple colours of colour zoning or banding; this zoning corresponds to the shape of fluorite`s crystals which makes a specimen more desirable to collectors.

G is for Garnet

Since the bronze age, garnet has been used as gemstones and abrasives.  Within the garnet group, there are different species that contain a variety of colours due to their different chemical compositions.  Pyrope and almandine are the most well known garnets are the red and purplish reds which when in a mix of both, are called rhodolites.  Grossular garnet is a species which includes orange hessonite and green tsavorite garnets.  Demantoid garnet is from the andradite garnet group which contains a unique horse tail inclusion, which is rare and expensive.  Demantoid garnets also occur without the horsetail, but are less desirable to collectors.  Spessartite is an orange-yellow variety of garnet mined in Madagascar.

H is for Hematite & Heat Treatment

Hematite is also spelled as haematite, is a mineral which is mined as the main ore of iron. Hematite is coloured black to steel, silver-grey, brown, reddish brown or red. Hematite is harder than pure iron and more brittle. Brown iron produces the golden yellow colour of tiger’s eye quartz and often occurs in tiger’s eye layered banding.

Gemstone colour and clarity can be improved with heat treatment.  Heat treatment is a common practice for many stone types including, ruby, sapphire, aquamarine, topaz and tanzanite. Heat treatment is the continuation of the process that occurs in the earth when the stone was originally formed.  Understand that treatments enhance a gem to let it's beauty shine, similar to the process of dying your hair or polishing your nails.  Aquamarine is heated to remove yellow tone and alter the green element to a more blue colour which is how most people imagine aquamarine to look.  Tanzanite would not exist unless heated to remove brown undertones and enhance the violet blue colour tanzanite is known for.  The world demand for gem quality corundum, ensures that ruby and sapphire are routinely heated to improve the clarity and colour.  Heat treatment is permanent in gemstones and is common practice.  Due to the large amount of heated gems in the world market, unheated ruby and sapphires with excellent clarity and colour can command a premium price.  Citrine is often amethyst heated to until the colour changes.  Ametrine is citrine partially heated to product gradient results; partly amethyst and part citrine.  All treatments should be disclosed to customers, however sometime they are not due to the commonality of the heating, so asking about treatments when buying a gemstone is certainly encouraged.  Knowing your gem is treated can prevent disastrous results with your jeweller.  Emeralds should not be heated, especially if they are treated with cedar oil, as the heat will remove the oil and could even cause the stone to fracture.  Diamonds must be protected with boracic acid when heating to prevent the surface from being burned on the surface or even completely burned up. So the lesson here is ask about treatment, if only to protect your potential investment.

I is for Iolite

Iolite is the transparent variety of Cordierite, used commonly as a gemstone.  Iolite that is gem quality is sometimes used as a reasonably priced substitute for Sapphire and Tanzanite.  Iolite has extreme pleochroism and is often a trichoic stone that shows three hues when viewed at different angles, violet, blue and colourless. Iolite colours vary from a bright sapphire blue to blue violet to yellowish gray to light blue as the light direction changes. Iolite is a much softer stone than sapphire, so it cannot stand the damage of daily use as ring but it's great for pendants and earrings. Iolite was likely the world's first polarising filter; Viking mariners used thin pieces of Iolite to navigate during their travels.