An obsession with opal (October's birthstone)

If you’re lucky enough to be an October baby, you have two birthstones to choose from – opal and tourmaline. Both are equally gorgeous but they’re radically different to each other and require different levels of care.

Let’s start with opal….

Perhaps one of the most beautiful gemstones around, opal is a hydrous silicate mineral that typically contains 6 – 10% water content. It is an amorphous mineraloid that forms via the deposition of mineral salts in the fissures of rocks. Australia is the world’s leading supply of opal, accounting for approximately 95% of the world’s opals, but the gem is also mined in Mexico, Brazil, Honduras, Ethiopia, the Czech Republic and parts of the U.S.A.

Rough opal from Ethiopia.

The name “opal” originates from the Greek word opallios, which meant “to see a change in color.” The Roman scholar Pliny used the word opalus when he wrote about this gem’s kaleidoscopic “play” of colors that could simulate shades of any stone.

Best known for its flashing rainbow colors called play-of-color, there are two broad classes of opal: precious and common. Precious opal displays play-of-color whereas the common version does not. Colour hues can range across the spectrum; an opal might display a single color, two or three colors, or all the colors of the rainbow. Black opal is considered to be the rarest, whereas white, gray and green are the most common colours to be found.

The characteristic “play-of-color” was explained in the 1960s, when scientists discovered that the mineral is composed of microscopic silica spheres that diffract light to display various colours of the rainbow.

Because of the gem’s high water content, it is a relatively soft gemstone, with a hardness of 5.5 to 6 on Moh’s hardness scale. As such, it is best suited for setting in earrings, pendants and brooches, where the jewellery is unlikely to encounter knocks and impacts. When used in a ring, the best designs have a bezel that protects the stone – instead of being placed in a prong setting that allows the edges of the stone to be exposed.

Like many gemstones, opal may be treated by impregnation with oil, wax or plastic. The safest way to clean this October birthstone is with warm, soapy water. Other cleaning methods might damage the gem or filler material. An extremely sensitive gemstone, opal can fracture if exposed to high heat or sudden temperature changes. Store your opal jewellery separately from your other jewellery to stop it being damaged by harder gemstones such as diamonds, rubies or sapphires.

Cushion cut Ethiopian opals in yellow gold stud earrings.

The world’s largest and most valuable opal, “Olympic Australis”, came from Coober Pedy, Australia in 1956, during the Olympic Games in Melbourne. Valued at $2.5 million in 2005, this gem measures 28cm long and weighs 17,000 carats (3.45kg).

Rare boulder opal in Coober Pedy, Australia.

Whilst most people associate this gem with Australia, Ethiopia is home to many fantastic specimens, which we have set in some gorgeous jewellery, including earrings, necklaces and pendants. If you’re obsessed with the iridescent colours of October’s birthstone, contact us to set and appointment to see what jewellery we currently have available.