November Birthstones: Citrine and Topaz

Citrine is a  popular and affordable member of the Quartz group (which includes Amethyst). The name is a derivation of the French word, for the lemon yellow colour that natural Citrines exhibit. Today though most commercial Citrines are actually heat treated Amethysts and are more of a golden than lemon yellow colour. Depending on the source deposit the heat treatment can produce  colours from yellow to gold to orange brown and red shades of transparent quartz. The final result being dependent on the level of heat applied. In ancient times, Citrine was carried as a talisman against the venom of snakes and scorpions. Today they are known in some cultures as the merchant's stone and are associated with success and prosperity.

Citrine 10x10 Square, 4.83 carats

The causal element  that imbibes natural quartz with its lemon yellow colour is a trace amount of Iron (approximately 40ppm). Natural (untreated) citrines are mostly a  pale lemon yellow to golden yellow colour, but recent demand has meant that almost all of the commercially available stones are now heat treated Amethyst, which exhibit a reddish tint to the overall yellow to golden hue of the stones.
Purchasing Citrine

Colour
While natural Citrine is much preferred over the Citrine produced by heat-treating amethyst, it is often hard to source such material as much of the rough currently available, is pre treated at source before it enters the cutting process. Paler more lemon yellow colours are preferable over the darker red tinted treated stones. Although personal preference is always the most important guide.

Citrine 10x5 Marquise, 0.90 carats

Clarity
Citrine, like Amethyst is an abundant member of the quartz group, and as such only  transparent examples  with excellent clarity, should be considered for facetted stones. A lower transparency can be considered for en cabochon cut stones

Cut
Citrines come in a wide range of calibrated shapes and sizes, constrained to a certain extent by the level of colour banding or zoning present in the stone. Portuguese cuts have become popular in recent years due to the additional brilliance added by the extra facets, which allow for more highly zoned stones to appear as consistent colours.
Mineable Deposits

The most important deposits of natural citrine currently in production occur in Brazil and Madagascar. Other locations include Argentina, Myanmar (Burma), Namibia, Russia, Scotland, Spain and the United States.

Citrine - Common Treatments
Natural Citrine is untreated and will typically exhibit some colour zoning, which can be partially dissipated with moderate heating. Most commercially available Citrine in the market have been produced by heat-treating Amethyst. Brazilian Amethyst will turns a light yellow colour at 878oF/470oC, and then a dark yellow to red brown at 1022-1040oF/550-560oC.
Important & Famous Citrine

While the piece in question has long been lost in the sands of time, around 1300 B.C the bejeweled breastplate of Aaron, contained a Citrine representing one of the 12 tribes (Naphtali) of Israel  - Exodus 28:15-30


Citrine is the birthstone for November, sharing this position with Topaz

   
Topaz Facts

There is limited consensus on where the name Topaz originated. The most plausible is that it is named after an island in the Red Sea formerly names Topazos, although today know as Zebirget. The complication arose from a time when all yellow, brown and even green stones were collectively known as “Topaz”.
Topaz comes in many colours naturally, including clear, brown, yellow, orange, red, pink and blue. The most common colour is yellow with a red tint; the most valuable is pink to reddish. The colouring agents are iron and chromium.

Mystic Topaz

The fine golden-yellow variety, known as Imperial Topaz, is relatively scarce. Topaz colours are rarely vivid, and as such the vast majority of today's commercially available cut stones have been enhanced.
Pure Topaz is colourless and transparent; it is only with the inclusion of impurities (trace elements) in the crystal lattice that colour is imparted to the stone. The common colours are brown, yellow, golden, orange, red, pink and blue. The colouring agents are iron and chromium.

Blue topazWhile natural blue topaz is rare, pale blue, pale yellow and white stones are commonly treated to produce the popular blue colours sold as: Sky Blue, Swiss Blue and London Blue

White Topaz:This naturally occurring colourless variety of Topaz has enjoyed tremendous interest in the past five years. As a natural, semi precious alternative to Diamond or White Sapphire, this stone is a cost effective alternative in everyday jewellery where a white stones is required

Mystic  Topaz:Displaying a kaleidoscope of iridescent colours, Mystic Topaz (also known as Mystic Fire Topaz), was first launched to the public in 1997. The popularity of Mystic Topaz increased dramatically when it was exhibited at the Tucson Gem Show in 2003.
Mystic Topaz is produced using a metallic vapor deposition coating process. This coating is applied to typically only the top (crown) of a facetted white Topaz. The treatment while hard wearing is only 1 micron or so thick, and can become abraded or even removed following polishing of the stone (when jewellery is cleaned), or from everyday wear and tear that will impart micro scratches to the stone surface, effectively cutting through the coating. The stones iridescent appearance changes depending on the light source and the viewing angle, adding to the fire effect of the treatment.

Pink Topaz

In addition to the iridescent fire colours, brilliant shade or blue, green and orange among others are also currently  being produced and marketed.

Imperial topaz
This the most sought after of all natural Topaz. Its rich golden colour is generally not enhanced by any kind of treatment.

Pink topaz
Natural pink Topaz is very rare and costly. The vast majority of pink topazes are heat-treated yellow stones that turn pink. Pink Topaz is also being produced in large quantities using a similar vapour depositing process as Mystic Topaz, this to satisfy the current worldwide demand for pink coloured stones.
 
Purchasing Topaz
Topaz is a very hard gemstone (8 on the Moh's scale) with a high refractive index thus making it ideal as an everyday gemstone.
 
ColourFor totally natural stones  the golden-yellow variety, known as Imperial Topaz,  yellow with a red tint or the most valuable pink to reddish stones are popular albeit at a price premium due to their scarcity. Without doubt the most popular colour is Blue topaz, followed by Pink and then the Mystic colours (all being enhanced stones)

Lighting

White Topaz

Topaz is a pleochroic stone, exhibiting different colour when viewed along different axis. No discernable difference is seen between natural and artificial light sources for viewing the stone.

Clarity
Topaz is a Type 1 clarity gemstone and as such only eye clean examples should be considered for purchase.

Cut
Topazes are generally  cut in the simple step cuts, although any cut can be encompassed. The cutting style for weakly coloured stones tends to be the round brilliant cut, which imparts more colour to the stone, or any of the cuts where additional facets have been added to enhance the lustre.

Topaz – Common Treatments
The most common treatments for natural rough Topaz  (colourless or very lightly tinted), is either neutron irradiation or  linear acceleration. which are use to create the Blue Topaz commonly available in most jewellers nationwide. Neutron irradiation  followed by stabilisation with heat is use to produce the Swiss Blue Colours (Baby Swiss, Light Swiss, Swiss, Top Swiss) through the strong blue colours (Korean Blue & Maxi Blue) to the dark London Blue Topaz (blue with a green/grey overtone) . The depth of colour in neutron irradiation is a function of  the length of time the rough material is exposed to the isotope Cesium 137. As reactor time is expensive so the darker colours  are sold at a premium over their light  counterparts. The perennially popular Sky Blue Topaz is enhanced using LINAC (linear acceleration) a less expensive enhancement method result in an Aquamarine coloured stone .
In  1997, a new type of enhanced Topaz made its appearance, the surface-enhanced Topaz, with colours described as blue to greenish-blue or emerald green.

The vast majority of pink Topazes are either heat-treated yellow stones that turn pink, or are the result of  a metallic vapor deposition coating process.

Displaying a kaleidoscope of iridescent colours, Mystic Topaz (also known as Mystic Fire Topaz), was first launched to the public in 1997. The popularity of Mystic Topaz increased dramatically when it was exhibited at the Tucson Gem Show in 2003. Mystic Topaz is produced using a metallic vapor deposition coating process. This coating is applied to typically only the top (crown) of a facetted white Topaz. The treatment while hard wearing is only 1 micron or so thick and can become abraded or even removed following polishing of the stone (when jewellery is cleaned), or from everyday wear and tear that will impart micro scratches to the stone surface effectively cutting through the coating. The stones iridescent appearance changes depending on the light source and the viewing angle, adding to the fire effect of the treatment.