Kosmochlor jade is the trade and laboratory term for jade-class material in which the chromium pyroxene kosmochlor (NaCrSi₂O₆) constitutes a substantial portion of the rock, either as the dominant pyroxene or in significant solid solution with jadeite. It is a legitimate variety of jade under modern nomenclature, alongside jadeite jade, omphacite jade (also called blue water jade or oil green jade in parts of the trade) and nephrite.

Distinguishing characteristics

Kosmochlor is denser and more strongly refractive than jadeite. Specific gravity ranges from approximately 3.55 to 3.65 against 3.30 to 3.38 for end-member jadeite, and refractive indices run from about 1.74 to 1.78 against 1.66 to 1.68. Where the bulk pyroxene is kosmochlor-rich, the polished slab will read consistently above the standard jadeite values on the refractometer spot test, and density measurement on a hydrostatic balance will fall outside the jadeite range.

Colour in kosmochlor-rich material is typically a deep, saturated chromium green, frequently darker than the much-prized imperial green of jadeite. In some pieces the green is so dense it reads as near-black under most lighting conditions, brightening dramatically with strong directional illumination. Mottled or marbled patterns are common, with chromite cores and serpentine matrix visible on careful inspection.

Origin

Most gem-grade kosmochlor jade originates in the jadeite tract of Kachin State, Myanmar, particularly the Tawmaw and Hpakant areas. Smaller occurrences are documented in the Itoigawa-Omi region of Japan, the Motagua Valley of Guatemala, the Polar Urals, and a handful of other high-pressure metamorphic belts where serpentinite-hosted jadeitites have formed.

Trade nomenclature and historical context

Older trade literature used the term chloromelanite for very dark, dense, chrome-rich pyroxene jade. Modern usage retains chloromelanite for some authors specifically as a kosmochlor-aegirine-jadeite mixture, but the term is inconsistent across reference works and is being supplanted by precise mineralogical reporting.

GIA and CIBJO permit jadeite, omphacite and kosmochlor to be reported simply as jade when the dominant constituent has been identified. A modern report will typically read natural jade followed by either jadeite, omphacite or kosmochlor, with treatment status (none, polymer-impregnated, dyed) given separately.

Identification in practice

Spot refractive index above 1.70, density above 3.5, and a chromium-dominant absorption spectrum with strong bands in the red are presumptive of kosmochlor. Raman spectroscopy gives a clear separation, with kosmochlor showing characteristic Si-O stretching modes shifted from those of jadeite. LA-ICP-MS or quantitative SEM-EDS confirms the chromium content directly. Polariscope behaviour follows that of an aggregate, with no extinction, identical to other jadeitic stones.

Kosmochlor jade is subject to the same treatment risks as jadeite. Acid bleaching and polymer impregnation (Type B) and dyeing (Type C) have all been reported on lower-grade kosmochlor-bearing material. Independent laboratory testing is essential at any meaningful price point.

Market position

Untreated kosmochlor jade of even saturated colour and translucent ground commands strong prices in the Asian market, although typically below comparable imperial green jadeite of similar transparency. The depth of colour can mask translucency, and very dark stones are sometimes cut as carvings or thick cabochons rather than thin transparent pieces. The material is most often encountered in carvings, bangles and signet-style cabochons.