Moonstone

Moonstone's beauty lies less in body colour than in adularescence, the floating sheen created by light scattering from microscopically thin alternating layers of feldspar within the stone. The most prized combination, closely associated with Sri Lanka, is a near-colourless, highly transparent body with a strong electric-blue sheen. Silvery and white sheens are more common and more affordable, and body colours also include grey, cream, peach and brownish tones from other sources. The blue effect is directional, rolling across the dome as the stone moves. Some moonstones additionally display a cat's eye effect or, rarely, a star. Fine blue-sheen material has become scarcer over the years, adding to its desirability.

The finest moonstones combine high transparency, a clean interior, and strong blue adularescence that is centred and lively on the dome. Semi-transparent to transparent stones outrank opaque ones, and a sheen that only appears at extreme angles is less valued than one visible in normal wear. Characteristic internal marks of moonstone include tiny stress fissures known in the trade as centipedes; heavy inclusions dull the glow. Cabochon proportions matter, since a well-domed, symmetrical cut focuses the effect. Fine Sri Lankan blue-sheen moonstone in larger sizes is genuinely scarce and priced accordingly, while attractive silvery stones remain accessible. Judge moonstone in person, moving it under light, rather than from static images.

Moonstone is typically untreated: the adularescence is entirely natural and no routine enhancement exists for the fine material. Coatings or impregnations occasionally appear on low-grade stones and, like every treatment, should be disclosed at every stage of sale under international trade standards such as CIBJO's Gemstone Book (Blue Book). The buyer's practical concerns are identification and substitution, opalescent glass, synthetic spinel with a sheen-like effect, and other feldspars such as labradorite (including the material sold as rainbow moonstone) can be confused with orthoclase moonstone. A gemmological laboratory can confirm species and natural character quickly. For fine blue-sheen Sri Lankan stones commanding significant prices, documentation from a recognised laboratory is a sensible safeguard.

Sri Lanka is the origin most celebrated for fine moonstone, and Meetiyagoda in the island's south-west is the locality synonymous with the gem: its shafts and pits have long produced near-transparent moonstone with the coveted blue sheen. Moonstone also occurs elsewhere on the island among the wider gem gravels. India is another major producer, supplying much of the world's peach, grey and cat's-eye moonstone, and material comes from Madagascar, Myanmar and Tanzania. The moonstone mines of Meetiyagoda are a visitor attraction as well as a working source, and Sri Lankan blue-sheen stones remain the reference against which others are measured.

Moonstone needs gentler treatment than the corundum family: at hardness 6 to 6.5 with pronounced cleavage, it can scratch and chip more readily, so it suits pendants and earrings especially well, and rings benefit from protective settings and mindful wear. Never use ultrasonic or steam cleaners, clean with lukewarm soapy water, a soft cloth or very soft brush, and pat dry. Avoid knocks, sudden temperature changes and contact with harder gems in storage; keep moonstone jewellery in its own pouch. Remove rings for housework, sport and gardening. With this modest care, the gem's glow lasts indefinitely, and light repolishing can revive a dome dulled by years of wear.