Deep into the autumn when the trees start turning dark, the sky gets a little greyer, and the weather becomes a little cooler, people born in October can find the burst of colour they need in their October birthstones; Opal and Tourmaline. Both these stones radiate with a variety of hues, and this guide explores these gemstones’ rainbow-like beauty and underlying significance.
What Makes an Opal
Rough Australian Opal (Source: Wikimedia Commons)
Opal is made from water carrying silica (silicon and oxygen compound) that seeps into sedimentary rock. As the water evaporates, it leaves deposits of silica in the cracks of sedimentary rock. The silica deposit, once solidified over time, becomes an Opal.
There are two general types of Opal: precious Opal and common Opal.
Precious Opal contains sub-microscopic spheres in grid-like formations that reflect light in flashes of different colours all at once. This process is called “play-of-colour.” Common Opal, on the other hand, does not have play-of-colour, and they are opaque or waxy.
What Makes a Tourmaline
A mix of rough Tourmalines (Source: Gandhara Gemstones)
Tourmaline is actually a group of mineral species that share the same crystal structure but have different chemical compositions and physical properties. Silicon, boron, and aluminium are the most common elements. Combinations of magnesium, sodium, calcium, iron, and lithium, to name a few, result in a range of colours and other characteristics.
There are five general types of Tourmaline: schorl, dravite, uvite, liddicoatite, and elbaite. Schorl is the most common type, while most gemstone-quality Tourmalines are elbaite.
Where Opal is Mined
Australia is the world’s primary source of Opals. Rich Opal deposits were discovered in the Land Down Under around 1850. Since then, Opal mining operations have cropped up all over the country and continue to produce gemstone-quality Opals. In fact, Australia accounts for 95% of global Opal production.
In Australia, there are two major sites of Opal mines: Coober Pedy and Lightning Ridge.
Olympic Australis, the world’s most valuable Opal (Source: Opal Auctions)
Coober Pedy boasts the biggest Opal production by mass. The Olympic Australis, the world’s largest and most valuable Opal gemstone, was found in Coober Pedy. It weighs 17,000 carats (3.5 kilograms) and measures 280 millimeters.
Black Opal Ring (Source: Lillicoco)
Lightning Ridge, meanwhile, is home to the finest black Opals and is the largest producer in terms of value.
Other countries with significant Opal mines include Ethiopia, Brazil, Mexico, Sudan, Hungary, Indonesia, and the United States.
Where Tourmaline is Mined
The majority of gem-quality Tourmaline is mined from Brazil and Africa.
A Paraiba Tourmaline (Source: The Eye of Jewelry)
The Tourmaline mines in Brazil offer almost all the colour variants of this gemstone. This South American country has been a reliable source of Tourmalines since the 16th century. The states of Minas Gerais and Bahia provide most Brazilian Tourmalines today. Paraiba also stands out for its intense neon-blue Tourmalines that command the highest prices.
A Rough Watermelon Tourmaline (Source: Gandharagems)
Nigeria, Mozambique, Madagascar, Namibia, Tanzania, Malawi, Kenya, and Zimbabwe make up the Tourmaline-producing African nations.
The History and Significance of Opal
Ancient cultures revered Opals for their multi-coloured lustre. The Romans thought of the gemstone as a symbol of hope and love, while the Greeks believed it gave visions of the future and warded diseases.
The Arabs told stories of Opals brought to earth by lightning. Medieval Europeans regarded Opals as bearers of good fortune, because they shone with the colours of all the other gemstones, encapsulating all their virtues.
Victorian Opal Ring (Source: Lillicoco)
Opals enjoyed great popularity from Europe’s ruling class for their rarity up until the 19th century. Sir Walter Scott’s 1829 novel Anne of Geierstein cast it as a bringer of bad luck and death, leading to a 50% reduction in sales of Opals within a year. The discovery of Opals in Australia also reduced its rarity.
The History and Significance of Tourmaline
Tourmaline was mistaken for other gemstones like Emerald, Ruby, and Sapphire for ages. This went as far back as the 1500s when Portuguese and Spanish explorers traded goods for Tourmalines that they sent back to their royal masters in Europe. It wasn’t until the late 1800s that gemologists distinguished Tourmaline as its own mineral species.
China valued Tourmaline greatly for centuries, culminating in the Chinese-American trade around the turn of the 20th century. Pink and red Tourmalines from California mines went into the collection of Chinese Dowager Empress Tz'u Hsi.
Pink Tourmaline Ring (Source: Wiki)
Tourmaline has been associated with sleep, helping feverish children rest and awaken those in “the dream of illusion.” It was also believed to aid in finding good and rooting out evil.
Pink Tourmaline, in particular, is said to promote unconditional love and friendship as well as calm fears and anxieties.
General Tips on Buying and Maintaining Opal and Tourmaline
Antique Opal and Diamond pendant (Source: Pinterest)
Opal and Tourmaline follow the four C’s of valuing gemstones.
The play-of-colour intensity in an Opal is the most important aspect. The wider the range of play-of-colour covering a stone, the better. Dark backgrounds are preferred by collectors.
For Tourmaline, deeply saturated colours are more valuable, with pink and red Tourmalines being the most coveted of the common variations. The bright blue and greenish hues of Paraiba Tourmalines are the most expensive.
Quality light Opals are transparent, while quality dark Opals are opaque. Hazy backgrounds devalue an Opal of any kind. Opals that feature crazing (fine, web-like cracks caused by moisture) are also valued less.
Inclusions in Tourmalines are generally frowned upon unless they form a cat’s eye. Inclusions are only tolerated in dark, heavily saturated Tourmalines.
Fine Opals are best cut in a domed, cabochon style. Only the exceptional Opals get the free-form treatment to show off their fantastic play-of-colour.
Tourmalines are typically cut into long rectangles, and the orientation depends on its colour depth. Pale stones are oriented perpendicular to their crystals length, while dark stones are oriented parallel
Opals are low density gems, so large sizes aren’t too heavy to wear. An 8x6 mm cabochon Opal looks good and feels comfortable.
Tourmalines heavier than 5 carats become exponentially more expensive, as gem-quality stones of that size are much rarer than their lighter counterparts.
Opal is much less durable than most gemstones with its 5.5 Mohs hardness rating. It is sensitive to temperature changes, scratch-prone, and can shatter easily. It is not suited for rings unless placed in a protective setting. Store Opal jewellery in soft, moist cotton to avoid them drying out and getting crazing.
Tourmaline, on the other hand, is tougher with a 7.5 Mohs hardness rating. However, prolonged exposure to direct sunlight and heat can still damage it. Boxed storage separate from other stones is recommended.
Both gemstones should only be cleaned with warm water, mild soap, and a soft brush. Avoid any other cleaning solutions.