October Birthstone: Opal & Tourmaline Jewelry

October has two: opal and tourmaline. Opal is the older and more traditional association; tourmaline was added later and is now equally recognised.

They are strikingly different. Opal is cut as a smooth dome for the colours that move inside it; tourmaline is a transparent faceted stone that occurs in more colours than any other gem species.

Either is correct for an October birthday, so the choice can be made on which the recipient would actually wear.

More than any other gemstone species - green, pink, red, blue, yellow, brown, black and colourless all occur, and single crystals often run through two or three colours.

The trade names are worth knowing: rubellite for pink to red, indicolite for blue, verdelite for green.

That range is unusual among birthstones, because it means a tourmaline can be chosen to suit the person rather than accepted as whatever colour the month dictates.

A slice cut across a tourmaline crystal that grew pink at its centre and green at its rim, so the finished stone shows both colours in concentric bands.

Colour zoning like that would count as a fault in most gemstones. In tourmaline it is the entire point, and cutters orient the crystal specifically to show it.

Bi-colour and tri-colour tourmalines are characteristic of the species rather than a rarity within it.

At 7 to 7.5 on the Mohs scale it sits in the practical middle - comfortably wearable, and harder than opal, peridot or turquoise.

In a ring worn daily, a setting that protects the stone's edges is sensible, as it is for most coloured stones in that range.

As a pendant or earrings it needs no particular consideration at all.

Because tourmaline is pyroelectric and piezoelectric: it develops a static electrical charge when it is heated or put under pressure.

That charge attracts small particles, so a tourmaline picks up dust and lint more readily than other stones do.

It is a genuine property of the mineral rather than a fault, and it simply means the stone wants wiping a little more often.

Tourmaline is the easier gift if you are unsure, because you can choose a colour the recipient actually wears, and it needs no special handling.

Opal is the more distinctive choice - nothing else looks like it - but it wants a wearer who does not mind treating a piece with some care.

If the piece will be worn constantly and without thought, tourmaline is the safer of the two.

Multi-stone October designs do appear, and there is no problem in principle.

The practical point is that a piece is only as robust as the most delicate stone in it. A design combining opal and tourmaline has to be cared for on opal's terms.

That means no ultrasonic or steam cleaning, no soaking, and a gentle hand throughout.

Yellow gold is the traditional setting for opal and brings out the warm flashes in its play of colour. White metals give it a cooler, more contemporary background.

Tourmaline depends on the colour of the stone: white metals keep blues and greens clean, yellow gold warms pinks and reds, and rose gold sits very naturally beside rubellite.

Both stones appear here in 14K gold and platinum, so it is worth looking at a design in more than one metal.

Tourmaline is commonly heated to improve colour, which is a stable, long-established practice, and some material is clarity-enhanced.

Opal is generally not treated in the way faceted stones are, though some opal on the market is impregnated or backed to strengthen thin material.

Treatment is a stone-by-stone matter rather than a rule about a species, so check the individual listing if it affects your decision.

Treat any October piece as if it contains the more delicate of the two stones, which is the safe rule when a collection holds both.

That means warm water and a soft cloth, no soaking, and no ultrasonic or steam cleaning under any circumstances.

Keep both stones away from household chemicals, and store them where nothing harder is resting against them.