Madagascar labradorite is the gem variety of plagioclase feldspar (a calcium-sodium aluminosilicate) recovered chiefly from the Maniry, Bekily and Tulear region of southern Madagascar. The material is distinct from the classic dark Canadian Labrador goods: Madagascan stones include both transparent yellow to colourless feldspar and a strongly iridescent variety often marketed as rainbow moonstone, which is technically a sodium-rich plagioclase with adularescence rather than the orthoclase that defines true moonstone.

Yellow labradorite

The transparent yellow material is faceted into stones of medium to large size, frequently above five carats and sometimes well above twenty. Refractive index falls near 1.56 to 1.57 with a hardness of 6 to 6.5; cleavage is well-developed in two directions, requiring careful setting. The yellow colour is unenhanced in the bulk of commercial production and ranges from pale champagne to a richer butter-gold.

Rainbow labradorite

Strongly iridescent stones are cut as cabochons, with the labradorescence ranging from blue and gold to multi-spectral flashes. Trade nomenclature is loose: stones from Madagascar with a strong blue sheen are widely sold as rainbow moonstone, although gemmologically they are plagioclase feldspar rather than orthoclase moonstone. Disclosure of the correct species name on grading reports is the laboratory norm.

Trade and treatment

No commercial treatment is in regular use for Madagascan labradorite. The deposits are mined by artisanal methods, and the rough is exported predominantly to India and Thailand for cutting. The material is durable enough for pendants, earrings and protected ring settings but its cleavage and modest hardness recommend caution for daily wear pieces. Madagascan yellow labradorite is also one of the few feldspar varieties cut in calibrated sizes for jewellery houses producing matching suites.