June Birthstone

Natural pearls form entirely without human intervention — a wild mollusc deposits nacre around a naturally occurring irritant over years or decades, producing a sphere of 100% nacre. They are extremely rare today due to over-harvesting of pearl oyster fisheries in the 19th and early 20th centuries. Cultured pearls are initiated by a human-inserted nucleus (typically a bead of freshwater mussel shell for saltwater pearls) coated in nacre over 2–5 years in aquaculture farms. The resulting cultured pearl has a nacre coating of 0.3–3+ mm over the nucleus. Both natural and cultured are real pearls — the nacre composition and lustre are identical. GIA X-ray examination can distinguish them by detecting the nucleus. For the vast majority of consumers, cultured pearl is the only type available; natural pearls of significant size command extraordinary premiums at auction (hundreds of thousands to millions of dollars for fine specimens).

Fine alexandrite is genuinely rare — rarer than ruby, sapphire, or emerald of comparable quality. The original Ural Mountain deposits (Russia) are effectively exhausted for commercial production; new material from Brazil, East Africa, and Sri Lanka is available but typically shows weaker colour change or less saturated colour than the best Russian material. The specific combination of chromium chemistry and the host mineral beryllium aluminate (chrysoberyl) that produces the ideal alexandrite colour change requires a geological coincidence where both beryllium and chromium are available together — chromium is normally found in mafic/ultramafic settings that are low in beryllium. Most chrysoberyl deposits lack the chromium for alexandrite. Fine one-carat Russian alexandrite (strong green-to-red, good saturation, eye-clean clarity) can retail for $10,000–$60,000+ per carat, with fine specimens in larger sizes commanding higher prices at auction.

Moonstone's adularescence — the floating, billowing light that seems to glow from within the stone — is produced by interference of light from alternating lamellar intergrowths of orthoclase and albite feldspar within the crystal. When these alternating layers are thin enough (approximately 100–300 nm thick), they scatter light preferentially at blue wavelengths and produce an interference colour that shifts across the stone's surface as the viewing angle changes. This gives the appearance of a light source moving inside the stone. The quality of adularescence depends on the thickness of the layers: very thin layers produce a blue sheen (most valued, often from Sri Lanka); thicker layers produce a white to yellowish glow. Sri Lanka produces the finest blue-adularescent moonstone; India produces abundant moonstone with white to yellow adularescence; the difference is one of market preference and layer thickness in the crystal structure.