White Valentine’s Special | A Guide to White Gemstones
Moonstone · Opal · Mother of Pearl
What do you associate the month of March with? For me, it’s a romantic month which reminds me of pure, snowy white hues, as it is the month of White Day (also known as White Valentine’s Day) celebrated on 14 March in Japan.
In gemology, “white” gemstones are not necessarily opaque, solid white. For example, “white diamonds” are actually colourless diamonds. White gemstones come in all sorts of enchanting shades and lustre – some are pearlescent, some are translucent, some are milky white, while some are iridescent.
In this blog entry, let’s talk about a few of my favourite white gemstones that share the same beautiful colour-shift quality: moonstone, opal, and mother-of-pearl.
The moonstone is well known for its dreamy shimmer reminiscent of moonlight, thus its name. In fact, the moonstone is associated with moonlight in many cultures, whereas Hindu mythology has it that the moonstone is made of moonbeans! This remarkable gem also has the romantic moniker “Lover’s Stone” and is one of the birthstones of June and the 13th anniversary stone.
A fun myth: Many used to believe that if you held a moonstone in your mouth during a full moon, you could see the future!
A raw moonstone and a moonstone cabochon.
Image credit: GIA.edu
Moonstone is a type of gem-quality feldspar – a group of closely related mineral species containing sodium, calcium, potassium or barium – the most widespread and some of the most diverse minerals in the earth’s crust.
The characteristic ethereal glow of the moonstone is known as “adularescence”, a visual phenomenon due to the scattering of light in the stone’s internal structure.
Moonstones with a colourless, semi-transparent to almost transparent appearance free from visible inclusions, and carrying a vivid blue adularescence known as “blue sheen” in the industry, are the most sought-after. The finest moonstone has a glassy purity with a lively electric blue shimmer. As inclusions could interfere with the adularescence, a good moonstone should be nearly transparent and free of inclusions as much as possible.
That being said, moonstone can actually come in a wide range of colours: white, green, yellow to brown, or gray to nearly black. As for the adularescent effect, it can be blue, silver or white.
As you might recall seeing moonstones in pictures and real life, they are most commonly cut in cabochon style, meaning that they are shaped and polished with a smooth, curved surface, the reason being that the cabochon form best displays the stone’s phenomenal, shifting colours and adularescence. The cabochon profile should also have considerable depth, as flat cabochons do not show its signature sheen well.
However, faceted moonstones have also become increasingly common. Faceted cuts can heighten the stone’s brilliance and tend to hide any possible inclusions.
Maintenance and care:
Moonstone ranks 6.0 to 6.5 on the Mohs Hardness Scale, meaning that it has poor toughness and is less durable than sapphire, diamond, or amethyst. If accidentally hit against a hard surface, moonstone is susceptible to scratching and chipping. Due to its more vulnerable nature, moonstones are often set into pendants, earrings, and brooches. As moonstone is typically not treated, it is safe to clean with warm soapy water. Avoid ultrasonic or steam cleaners.
Ever imagined capturing fireworks in a gemstone? If that could happen, it would pretty much be what the opal looks like.
Opal boasts a dramatic “play-of-colour” that has inspired comparisons to fireworks, fire, galaxies and volcanoes by writers. Bedouins once believed that opal held lightning and fell from the sky during thunderstorms; whilst ancient Greeks thought opals bestowed the gift of prophecy and protection from disease. Opal is the traditional October birthstone, and is also given to celebrate the 14th wedding anniversary.
Image credit: GIA.edu
Opal is the product of seasonal rains drenching dry ground in regions such as Australia’s Outback. The rainwater carries dissolved silica (a compound of silicon and oxygen) downwards deep into the crevices of ancient underground sedimentary rock. When water evaporates during dry periods, the silica-rich water rests into a gel and hardens, and solid silica deposits are left behind in the form of tiny silica spheres, forming opal.
There are two broad classes of opal: precious and common (also known as potch opal). Precious opal displays a spectacular shifting colours in rainbow hues – a phenomenon known as “play-of-colour”, while common opal does not.
As mentioned above, opal’s structure comprises tiny silica spheres. These spheres are stacked in a grid-like pattern on top of each other – one could imagine a boxful of ping pong balls. As these silica spheres vary in placement and size, they cause lightwaves to diffract or bend differently, breaking up the light into the colours of the rainbow, known as spectral colours, resulting in a fabulous “play-of-colour”. No two opals are exactly alike.
Image credit: Broken River Mining
There are mainly 5 varieties of precious opal:
White or light opal: Translucent to semi-translucent, with play-of-colour against a white or light grey background colour, called bodycolour
Black opal: Translucent to opaque, with play-of-colour against a black or other dark background. Black opal is the most rare and highly valued form of opal.
Fire opal: Transparent to translucent, with brown, yellow, orange, or red body colour. This variety — which often doesn’t show play-of-colour — is also known as “Mexican opal.”
Boulder opal: Translucent to opaque, with play-of-colour against a light to dark background. Fragments of the surrounding rock, called matrix, become part of the finished gem.
Crystal or water opal: Transparent to semi-transparent, with a clear background. This type shows exceptional play-of-colour
Precious opals are often cut into irregular shapes that keep as much play-of-colour as possible.
Maintenance and care:
The safest way to clean opal is with warm, soapy water. As opal could be treated by filling with oil, wax or plastic, other cleaning methods might damage the opal or filler material. Avoid exposure to high heat or sudden temperature changes, as even natural opal can fracture under such extreme conditions.
In terms of the hardness, opal ranges from 5 to 6.5 on the Mohs Hardness Scale. Opal jewellery should be stored by itself to prevent it from being scratched by other harder gems, such as diamonds, rubies, sapphires and emeralds.
Don’t we all love the lustrous, quiet elegance of pearls? But how about mother-of-pearl? What exactly is it – is it truly as the name suggests, the “mother” of pearls?
Like pearls, mother-of-pearl is a type of “organic gemstone” – precious treasures from the ocean. Due to its beauty and often dreamy colours, mother-of-pearl is prized by many jewellery brands and featured as the star in many jewellery designs. It is also commonly used as decorative inlays for craftwork, home ornaments and even architecture. Mother-of-pearl is also one of the birthstones of June alongside moonstone.
Also called “nacre”, mother-of-pearl is a calcium carbonate layer produced by some molluscs as an inner shell layer. Pearls are essentially composed of the same material.
As the interior of shells, mother-of-pearl generally come with different growth patterns and a variety of lustrous shades. Some are translucent, some carry a dreamy iridescence or shine, while some could be more opaque.
Much like pearls, mother-of-pearl comes in many natural colours, including white, cream or off-white, pink, grey, silver and even gold.
Mother-of-pearl is often used as inlays for jewellery, retaining the original texture of the surface for a more organic, rustic feel. It can also be polished into a high-shine cabochon to let the mesmerising pearlescence truly shine through, such as this gorgeous Sakura collection from Laine Jewellery with petals made from handpicked mother-of-pearl.