Buying Guide

Of all the gems produced by Sri Lanka, moonstone may be the most ethereally beautiful. Its defining characteristic — a soft, floating blue glow that seems to drift beneath the surface as the stone is moved — has captivated jewellers and collectors for centuries. The Romans believed moonstone was formed from moonlight itself. Today, gemologists know it is caused by a phenomenon called adularescence, and they know that the finest examples in the world come from one place: Sri Lanka.

Yet moonstone is also one of the most misunderstood gems in the market. Many buyers are confused by the range of quality available, by the difference between Ceylon moonstone and lower-grade material from other origins, and by the fact that "moonstone" is sometimes used loosely to describe other feldspar gems with superficially similar appearances. This guide gives you the knowledge to identify, evaluate, and buy Ceylon moonstone with confidence.

What Creates the Glow?

Moonstone is a variety of feldspar — specifically orthoclase, sometimes with albite. Sri Lankan moonstone is typically potassium-rich orthoclase feldspar with alternating thin layers of albite intergrown within it. When light enters the stone, it scatters between these alternating layers, producing a soft, billowing glow that moves as the stone is rotated. Gemologists call this adularescence, named after a classic locality for the gem in Adular, Switzerland.

The colour of the adularescent glow is the primary quality indicator. The finest Ceylon moonstones show a vivid blue glow — sometimes called "blue flash" — against a colourless or near-colourless body colour. This combination of colourless body and strong blue adularescence is what makes Sri Lankan moonstone the benchmark against which all other moonstone is measured. Moonstones from India tend to show a more brownish body colour with a more orange or milky glow. Those from Madagascar and Myanmar are typically less transparent and show weaker adularescence.

Evaluating Quality

Adularescence strength is the most important factor. The glow should be vivid, concentrated, and easily visible when the stone is held under a light source and rotated. A weak or milky glow indicates lower-quality layering between the feldspar components. The strongest glow appears as a concentrated bright spot or shaft of blue light that moves with the stone.

Body colour should ideally be colourless or as transparent as possible. The more transparent the body of the stone, the more dramatic the contrast with the adularescent glow, and the more visually striking the result. Yellow, brown, or opaque body colours reduce the quality and value significantly.

Transparency distinguishes fine moonstone from lower grades. Top-quality Ceylon moonstone is semi-transparent — you can see into the stone, and the glow appears to float inside it rather than on the surface. Opaque or translucent material is significantly less valuable.

Cut is critical for moonstone. Moonstone is almost always cut as a cabochon — a smooth, domed shape without facets — because this shape best concentrates the adularescent glow at the top of the stone. The dome height must be calibrated precisely: too flat and the glow weakens; too steep and the stone looks dark. A well-cut moonstone has the glow perfectly centred when viewed from directly above.

Gemological Properties

Moonstone has a Mohs hardness of 6 — lower than most other precious gems — and two directions of perfect cleavage. This means it requires careful handling in jewellery. Settings should protect the stone from sharp blows, and moonstone rings require more care than sapphire or ruby rings. Rings featuring moonstone are best worn occasionally rather than daily.

The refractive index of Ceylon moonstone is 1.518–1.526, and specific gravity is approximately 2.57. These readings, combined with the characteristic adularescence, make moonstone straightforward to identify with basic gemological instruments. There are few convincing imitations — synthetic moonstone exists but shows a more uniform glow without the natural depth and variation of genuine material.

Price Guide

Ceylon moonstone prices are driven primarily by adularescence quality and transparency:

• Commercial quality (milky, weak blue flash): USD 10–50 per carat
• Good quality (clear body, good blue flash): USD 50–150 per carat
• Fine quality (colourless, vivid centred blue flash): USD 150–400 per carat
• Top collector quality (transparent, intense blue, large size): USD 400–1,000+ per carat

Fine moonstone above 10 carats with exceptional transparency and a vivid centred blue flash is genuinely rare and commands premium prices. Unlike sapphire, moonstone is generally not certified by major laboratories — the purchase is based on visual assessment rather than documentary proof of origin.

Buying Advice

When buying Ceylon moonstone, view the stone under a single directional light source — a window or a pen torch. Rotate it slowly and observe the glow. It should be vivid, blue (not white or orange), and concentrated rather than diffuse. The body of the stone should be as colourless and transparent as possible. Look through the stone against the light — the more transparent it is, the higher the quality.

Sri Lanka's moonstone mining areas are concentrated in the south of the island, particularly around Meetiyagoda in Matara District — a location known locally as the "moonstone capital of the world". Buying directly from reputable dealers in Galle, Matara, or Colombo gives you the best access to genuine Ceylon material, but always ask to see stones under controlled lighting before committing to a purchase.

Disclaimer: Price ranges are approximate market references only. Always consult a certified gemologist before making any significant purchase. CeylonGemLuxury does not sell gemstones directly.