If Australian opal is mined from indigenous sacred sites, then like anything else removed from the site, it is unlucky. That is Aboriginal Magic, not Opal Magic.
All opals from everywhere are formed in the presence of water: it is the combination of water and silica being compressed together at high pressures that creates the opalescence and the fire. Trace impurities of other minerals determine the colouration.
It is unwise to get opals wet: if they are not covered in something protective there is a risk that the water might seep into the stone and ruin the "fire". That might be the reason why your people recommend oiling them - I have never, ever heard that mentioned before today, and I hang around jewellers and used to hang around opal miners. My opals, many inherited from my grandmother who had many of them by the 1920s and 30s, have lasted for decades and because I haven't let water damage the stones, they are perfectly fine without ever having seen a trace of oil in their lives.
You are so right, about the indigenous sacred sites. But I did read that Australian opals are formed in dry silica. Anyway, I found something very interesting: from opalsdownunder.com, specialists in my book.
"Myth: Opals need to be soaked in water occasionally to prevent cracking.
Fact: Australian Opal is non-porous and therefore impervious - it cannot soak up water, oil, or anything else. The water content in an opal is determined during the formation of the stone, with water molecules locked into tiny voids within the opal's crystalline silicon structure. Soaking your opal in water will do nothing to increase the life of your opal. However, wetting an already cracked stone will temporarily hide the fault, a fact which may have contributed to prolonging this myth. It's important to note that opals should never be cleaned in an ultrasonic cleaner, as the extreme vibrations may cause the opal to crack. However, Hyrdrophane Opal (usually sourced from Ethiopa) is now gaining in popularity, but we do not cut or stock it.
Myth: Opals are extremely fragile and will break very easily.
Fact: It's true that opals are more fragile than most gemstones, however they're not as fragile as some people imagine. Opals are about the same hardness as glass, so imagine you're wearing a piece of glass and you'll get the idea. Avoid heavy manual labour, moving furniture, sport, gardening or any other vigorous activity where your opal might impact with hard surfaces and your opal will enjoy a long and happy life. With a little common sense it's easy to take care of opals. Boulder opals and opals with a low cabochon are sturdier and less easy to damage.
Myth: Opals need to be rubbed with oil (baby oil or olive oil) or glycerin occasionally to prevent cracking.
Fact: Rubbing your opal with oil will do nothing more than make your opal oily. Australian Opals are non-porous and do not soak up liquids, therefore baby oil will not increase the life of your opal.
Myth: Opals are unstable and prone to cracking.
Fact: Most opals are extremely stable and never crack. Stable opals have a water content of approximately 3 to 10 per cent, and any unstable material will normally crack soon after being mined. By the time the opal travels from the mines, and is processed, cut and polished, any unstable material is usually identified and weeded out.
Myth: Water damages solid opals. Never clean your opal with water or get your opal wet. The opal will expand and crack.
Fact: Solid opals cannot be damaged by getting wet. Most Australian precious opals contain around 5-6% water, and immersing a solid opal in water will do no damage whatsoever. However, doublet and triplet opals (non-solid, partially man-made layered stones) can be damaged by prolonged exposure to water. Water penetration can eventually cause the glue to deteriorate and the layers to separate, causing the opal to take on a foggy, grey, or cloudy appearance. This fact is the origin of the 'never get your opal wet' misconception.
This is from opalsdownunder...
http://www.opalsdownunder.com.au/learn-about-opals/introductory/opal-facts-myths
AND! I love moonstone too! I have a few pieces of jewelry with moonstones in it. 