Blue gemstones are synonymous with royalty, luxury and, quite frankly, good taste. Sapphire, a gemstone known for its rich velvety blues, is September’s birthstone however, there is an abundance of other blue minerals available in a variety of shades and tones. Made In Earth carries five blue gemstones as an alternative to sapphire; iolite, topaz, aquamarine, kyanite and tanzanite, each with their own identifying colours and properties.
Iolite
Improperly known in the trade as ‘water sapphire’, iolite is the blue/violet variety of cordierite. Fine iolite can display a deep blue-violet through to a pale blue-violet colour with some more vivid stones challenging the likes of tanzanite. This colour, derived from iron, is naturally occurring and cannot be enhanced by man unlike some other blue hued rivals where treatments are often essential to alter colour and clarity to a more desirable and saleable level.
With a hardness of 7- 7.5 on MOH’s scale it is suitable for rings as well as other forms of jewellery and is often an affordable substitute for tanzanite and sapphire when rich colour and clarity are present. Although eye-clean stones can be found, they are becoming harder to find in larger carat sizes, so it’s typical to find eye-visible healed fractures in stones over 5 carats. Iolite is a uniquely coloured, affordable and abundant mineral and yet, it is still one of the lesser known and underappreciated gems.
Topaz
Relatively inexpensive compared to the likes of sapphire, blue coloured topaz is the most common variety found in retail stores and consumers aren’t always aware that stones are almost always colour enhanced. In nature, topaz is most commonly colourless with naturally occurring strong blue gems being extremely rare. In the marketplace they are plentiful due to colour treatments being common practice. A combination of radiation and heat has been used to produce blue hues since 1970. This irradiation is perfectly safe as a “cooling down” period is taken into account. This is an acceptable treatment and should be assumed for all blue coloured topaz gemstones.
Although this stone measures a high 8 on MOH’s scale of hardness it is not necessarily a ‘tough’ stone due to its perfect basal cleavage. Cleavage refers to a stone’s tendency to cleave or split along certain crystallographic planes due to a weakness in their atomic bonds. Although a gemstone doesn’t necessarily become weak because of perfect cleavage, the gem cutter and jeweller must practice caution to ensure cleavage does not occur.
When cut and faceted, topaz gemstones are often free of visible inclusions and because of their elongated crystals, stones are mostly fashioned into pears, ovals and rectangles to yield more carat weight. Topaz is typically favoured for its clarity and evenness of colour.
Aquamarine
Reminiscent of the cool sea green of the oceans and the icy blue tones of the sky, the name aquamarine originated from the Latin ‘aqua marina’ which translates to ‘water of the sea’. One of the many famous coloured varieties of the Beryl family, aquamarine owes its fresh blue hue to ferrous Iron Fe2+ and colours can range from pale-blue, mid-blue to greenish-blue. Treatments aren’t uncommon; heating can remove the greenish colour component to produce a more blue appearance.
Ranked at 7.5 – 8 on MOH’s scale of hardness makes aquamarine perfect for rings as well as other types of jewellery. Faceted stones have a fine luster and well-cut stones show brilliance. It’s not uncommon to find big stones that are eye-clean but their inclusions can be quite the feature in an interesting piece of jewellery. A typical and diagnostic inclusion of aquamarine is called ‘rain’; elongated hollow tubes running parallel to the crystal axis. As most of our clients enjoy the very natural aesthetics of crystals we sell stones with typical beryl inclusions and varying colour ranges rather than the eye clean gemstones that can be confused for topaz.
Kyanite
With a name that was derived from the Greek word kyanos, meaning “deep blue”, kyanite is known for its undeniably similar hue to the rich blue of Ceylon Sapphires although these gems are worlds apart. Kyanite crystals are prismatic or tabular with a fibrous/ bladed structure down the length of the crystal. This physical characteristic is responsible for internal colour banding and cat’s eye chatoyancy when stones are cut en cabochon. Kyanite’s physical and optical properties vary with direction. The direction of hardness parallel to the crystal axis is 4 – 5.5 and perpendicular is 7 – 7.5. This phenomenon is further enhanced by the stone’s perfect cleavage and in kyanite’s case, the cleavage occurs parallel to the length of the crystal in line with the bladed structure.
Due to these properties, to preserve the stone during the cutting process kyanite is typically cut into an oval shape. When deep stones are cut with a modified brilliant cut, they can show brilliance which is further intensified by the stone’s delicate internal colour banding.
Tanzanite
The rock star of the gemstone world, Tanzanite was made famous by Tiffany & Co shortly after its discovery in 1967. Tanzanite is a variety of Zoisite and owes its unique colour to trace elements of vanadium. Tanzanite’s colour can vary from a vivid blue to lavender purple but it’s this stone’s pleochroism that sets it apart from other similarly coloured gems.
Pleochroism refers to a crystal’s ability to display different colours depending on the crystal axis it is viewed from. Some faceted stones may show flashes of both blue and reddish purple when slowly tilted from side to side. This remarkable colouring attribute has helped it gain popularity, rivaling the likes of the classic blue and purple sapphires.
The challenge for stonecutters is to capture this amazing colour play whilst still retaining carat weight and clarity when orienting the crystal for faceting. Vivid blue tanzanite is the most desirable but as the blue colour is viewed from the short axis of the crystal it is not the most economical orientation to cut from to gain the most yield out of the rough. For this reason most tanzanite gemstones exhibit a more purple/violet colour.
Typically found in a yellowish-brown ‘bug-juice’ colour, the majority of blue tanzanites on the market have been subject to heat treatment to cancel out the yellowish-brown tones and further enhance the blue/violet hues. Although it is possible to find naturally occurring blue crystals, it is extremely rare.
Tanzanite can be found in eye-clean quality but are known to have fine healed fractures, this along with a hardness of only 6 ½ (Moh’s scale), paired with perfect prismatic cleavage, make it a problematic mineral to cut and set and caution should be taken when wearing tanzanite jewellery.