Halley’s Comet Opal: The most colourful gemstone on Earth
Opal is one of the most sought-after gemstones globally. And why would it not be? After all, a nice expensive opal can flash every hue in the light spectrum with an intensity and colour quality that can surpass a diamond’s fire! Now you know what’s probably more brilliant than a diamond, right?
You’ve probably heard of the ‘Halley’s Comet opal’. The enormous stone, about 2000 carats in weight and the size of a man's clenched fist, was discovered on November 3, 1986, at an opal field in Australia, located at the bottom of what is known as the Lunatic Hill. The credit for the discovery goes to a group of five opal miners known as ‘The Lunatic Hill Syndicate’. As obvious as it can get, this opal was named after Halley’s comet, which happened to pass over Australia that same night. This rare specimen has garnered great fame and is included in the Guinness Book of World Records as the world’s largest uncut black opal nodule. Now, that’s interesting, isn’t it? Here’s a glimpse at this gorgeous gemstone.
The colours of Halley’s Comet Opal
Halley’s Comet opal is a fine-quality, black, knobby opal (a natural opal with a lumpy shape found only at the Lightning Ridge, Australia) formed some 20 million years ago! An old one for sure. Measuring 100 × 66 × 63 mm and weighing 1982.5 carats, it is about an inch across at its widest point. This band of black opal displays a floral pattern with green, yellow and blue-violet colour swatches. This colour ring perfectly centres the fist-sized opal globe.
In addition, the opal exhibits the property of play-of-colour, wherein a spectrum of colours is created as light passes through the opal. This occurs because the opal has millions of microscopic spheres of the mineral silica organised in a network. These tiny, half-micron-sized spheres produce diffraction grating (division of light into different wavelengths), which creates a spectrum of colours. This is what makes the opal so stunning to see!
A ‘precious opal’ indeed!
Though Halley’s Comet opal might be the one garnering records, here, are two types of opal that may surprise you if you are just beginning to learn about them. ‘Fire Opal’ is a vibrant, transparent-to-translucent opal with a vivid background hue of yellow, orange or red that resembles fire. The next variety is ‘precious opal’, which, when moved, or when the light source is changed, displays iridescent hues (play-of-colour). A common opal’s colour, pattern and elegance may range from ordinary to common. But, they do not exhibit play-of-colour.
Halley’s Comet opal belongs to the precious opal category. With minimal imperfections, it is the largest opal and is now estimated to cost more than $1,700,000. The black opal’s origin, its distinctive colour pattern, large size and background are what make it so expensive.
The story of the Lunatic Hill
As already mentioned, the Halley’s Comet opal was found in the Black Opal Field at Lightning Ridge, Australia. Despite mining in the area since the early 1900s, no stone this big has ever been discovered. This opal field is a shallow flatland situated at the bottom of the Lunatic Hill. A mere 200 metres downhill from the current open cut, at a depth of 2–5 metres on an average, most of black opals were mined in earlier days. However, most local miners thought this depth was sufficient for easily mining black opals. Specifically, miners from the local group of miners called ‘Leaning Tree,’ who were mining in the 3-mile black opal field, claimed that anyone willing to climb the hill only to descend all the way down to where the opals are found was completely lunatic!
One day, a lone miner dug a mine shaft on top of the hill to try his luck. After digging a 20-meter-deep tunnel, he came across some of the most exquisite black opal stones ever mined in Australia. Since then, the locals named the ridge the ‘Lunatic Hill’. In fact, it’s on this same hillside that the Halley’s Comet opal was found at a depth of 20 metres! Whether they were lunatics or not, a few individuals dared to mine in this area, and the results were astounding!