Omphacite jade is jade composed primarily of the mineral omphacite — a sodium-calcium-magnesium-aluminium clinopyroxene with intermediate composition between jadeite (NaAlSi₂O₆) and the calcium-magnesium pyroxenes (diopside, augite). Together with jadeite jade and nephrite jade, omphacite jade is one of the recognised varieties of the broader gemmological category jade, and the three are documented as distinct in the GIA and Gübelin literature. Omphacite jade forms in the same high-pressure metamorphic environments that produce jadeite — eclogite-facies conditions at depths of 50 to 100 kilometres — and is often intergrown with jadeite, with the two minerals forming a partial solid-solution series. Compared to pure jadeite, omphacite jade tends to be deeper green to dark green in colour and slightly less translucent, and it occurs in a smaller subset of the deposits worked for the broader jade trade.

Mineralogy and composition

Omphacite has a complex composition that can be approximated as (Na,Ca)(Mg,Fe,Al)Si₂O₆, sitting between the sodium-aluminium endmember jadeite, the calcium-magnesium endmember diopside, and the calcium-iron-aluminium endmember hedenbergite-aegirine. Crystallographically it belongs to the C2/c clinopyroxene group at higher temperatures, with a transition to the P2/n group with cation ordering at lower temperatures. The compositional variation across the omphacite-jadeite-diopside-hedenbergite system is continuous, and the boundary between omphacite and jadeite — placed conventionally at approximately 80 per cent jadeite component — is a matter of geochemical convention rather than a sharp natural break.

The physical properties of omphacite jade are intermediate between jadeite and diopside. Refractive index is approximately 1.66 to 1.68 (jadeite is 1.65 to 1.68, diopside 1.66 to 1.72), specific gravity around 3.30 to 3.45 (jadeite 3.30 to 3.38, diopside 3.20 to 3.40), and hardness 6 to 7 on the Mohs scale. The toughness of omphacite jade is comparable to jadeite — exceptional for a stone of this hardness, owing to the felted-fibrous microstructure characteristic of jade-grade material.

Geological occurrence

Omphacite is the dominant pyroxene of eclogite — the high-pressure metamorphic rock formed when basaltic protolith is subjected to depths of 50 to 100 kilometres in subduction zones. Eclogite contains omphacite together with garnet, with rutile and other accessory minerals; the omphacite of typical eclogite is not generally of jade quality, occurring as scattered crystals within the rock. Jade-quality omphacite forms in particular sub-environments where the felted-fibrous microstructure necessary for jade toughness developed, and these zones are scarce within the broader eclogite-bearing terrains.

Documented sources of omphacite jade include certain zones in the Burmese jadeite deposits of the Hpakan region, where omphacite-rich rocks are intergrown with the more abundant jadeite-rich material; the Polar Ural jade deposits in Russia; and zones within the Motagua Valley deposits in Guatemala. The omphacite-jade output is generally smaller in volume than the jadeite output from the same deposits, and the material is sometimes marketed as a jade variety distinct from jadeite, sometimes folded into the broader jadeite trade depending on the regional convention.

Identification and disclosure

Distinguishing omphacite jade from jadeite jade is not trivial in the field but is straightforward in laboratory analysis. The Raman spectrum of omphacite differs from jadeite, and the chemical composition determined by electron microprobe or X-ray fluorescence resolves the question definitively. The two minerals have similar visual appearance, refractive index, and specific gravity, so visual examination alone is insufficient. The major laboratories — GIA, Gübelin, SSEF, GIT, and CIBJO-aligned facilities — report omphacite jade as a distinct variety on laboratory documents, with both the species (omphacite) and the variety (jade) named.

For commercial purposes, the distinction between jadeite jade and omphacite jade is sometimes meaningful and sometimes not. Within the high-end Chinese jadeite market, the jadeite-type material commands premium prices and the omphacite distinction matters; in the broader international jade trade, the visual character and treatment status of the piece matter more than the precise pyroxene composition. Buyers seeking traditional Burmese A-jade should ask for laboratory identification, particularly for higher-value pieces.

In the trade

Omphacite jade is most often encountered in carved decorative objects rather than in faceted gemstone form. The dark green colour and good translucency of the better material suit it to the same applications as fine jadeite — pendants, carved figurines, bangles, and decorative objects. Treatment status (A jade for untreated, B for polymer-impregnated, C for dyed) follows the same conventions as jadeite. Care follows standard jade protocols: gentle cleaning by mild soap and warm water, avoidance of ultrasonic and steam, careful handling around hard surfaces.

Further reading

• GIA Gems & Gemology — jadeite and jade articles
• Gübelin Gem Lab — jade reporting
• International Gem Society — jade reference