Opal
A hydrated silica showing shifting spectral colour, called play of colour. Soft, water-bearing and fragile.
Opal's colour flashes come from silica spheres diffracting light, which is a structural effect rather than a pigment.
It contains up to 20% water, so sudden temperature changes and very dry storage can craze it, a fault called crazing.
In Vedic astrology opal substitutes for diamond as the stone of Venus, which is why it appears more often in India than its fragility would suggest.
When you are buying
Opal is one of the few stones as delicate as pearl. Set it in a bezel, keep it out of ultrasonic cleaners, and do not leave it in a hot car.
Orient
The faint shifting rainbow that plays across the surface of a fine pearl, distinct from its lustre or its colour.
Gemstone
Any mineral or organic material cut for jewellery. Traditionally split into precious (diamond, ruby, sapphire, emerald) and semi-precious.
Bezel Setting
A metal rim wrapped around the edge of a stone or pearl to hold it. The most protective setting there is.
Pearl Care
Pearls are soft and porous. They need to go on last, come off first, and be stored apart from everything else.