Opal is the birthstone for the month of October, along with pink tourmaline. It is also the stone given on the 14th wedding anniversary. The name opal is thought to be derived from the Sanskrit upala, meaning “precious stone,” and later the Greek derivative “Opallios,” meaning “to see a change of colour.”
The opal’s characteristic changing colours was explained in the 1960s, when scientists discovered that it is composed of microscopic silica spheres that diffract light to display various colours of the rainbow.
The Opals country of origin is Australia. Rains soaked the parched Outback, carrying silica deposits underground into cracks between layers of rock. When the water evaporated, these deposits formed opal. Sometimes, silica seeped into spaces around wood, seashells and skeletons, resulting in opalized fossils.
Since Opal was discovered in Australia around 1850, the country has produced 95 percent of the world’s supply. Opal is also mined in Mexico, Brazil, Honduras, Ethiopia, the Czech Republic and parts of the U.S.
The water content of opal gems can range from three to 21 percent—usually between 6 and 10 in gem-quality material. This, combined with hardness of only 5.5 to 6 on the Mohs scale, makes opal a delicate gemstone that can crack under extreme temperature, dehydration, or direct light.
The name "tourmaline" comes from the Sinhalese words tura mali, which mean "stone of mixed colours." As its name implies, tourmaline stands apart from other gemstones with its broad spectrum of colours in every shade of the rainbow.
Tourmaline is not one mineral, but a fairly complex group of minerals with different chemical compositions and physical properties. Certain trace elements produce distinct colours, resulting in many varieties.
The lighter coloured stones are commonly called Pink Tourmaline and the darker reddish-pink or red stones are known as Rubellite or Red Tourmaline. It is specifically the pink tourmaline which is the birthstone of October.
Rubellite or red tourmaline is caused by manganese, but if the colour becomes less vibrant under different light sources, it may be called pink tourmaline.
Tourmaline is mined in Brazil, Sri Lanka, Nigeria, Mozambique, Madagascar, Afghanistan, Pakistan and the U.S.—primarily Maine and California.
Tourmaline is desirable because of its sheer range of colour options. Combined with a good hardness of 7 to 7.5 on the Mohs scale, tourmaline makes very wearable birthstone jewellery.
One of this gemstone’s most impressive traits is its ability to become electrically charged through heat and pressure. When charged, tourmaline can act as a magnet by oscillating, and by attracting or repelling particles of dust.