Kosmochlor jade (“maw sit sit”) (8.0 cm across along the base) from the Hpakan-Tawmaw Jade Tract (near-latest Jurassic, 147 m.y.) of northern Burma.

Maw sit sit is a very rare, complex, polymineralic metamorphic rock. Minerals reported in this material include chromite (metallic black, FeCr2O4), kosmochlor pyroxene (emerald green to dark green to black, NaCrSi2O6), chromian jadeite pyroxene (green, Na(Al,Fe,Cr)Si2O6), chromiferous arfvedsonite amphibole (green or gray, Cr-bearing NaNa2Fe5Si8O22(OH)2), symplectite (green, a finely-crystalline mineral mix of mostly chromian jadeite). Reported matrix minerals include thompsonite zeolite, albite feldspar, or serpentine.

Maw sit sit formed under high pressure and low temperature conditions at the rim of serpentinized, chromiferous mantle peridotites. The peridotites were emplaced by obduction as oceanic lithosphere was subducting beneath the Burmese portion of southeastern Asia during the Mesozoic.

Geologic unit: northeastern end of the Hpakan-Tawmaw Jade Tract, Hpakan Ultramafic Body, Naga-Adaman Ophiolite.

Age: Syngenetic zircons indicate that Burmese jades formed at 147 Ma (late Tithonian Stage, near-latest Jurassic. The serpentinite host rocks formed (metamorphic age) at 163 Ma (Middle Jurassic). Older literature interprets Burmese jadeitite as Tertiary in age, hosted by Late Creatceous to Eocene serpentinized peridotites.

Locality: apparently an alluvial clast derived from the Namshamaw Deposit ("Namshamaw Dike"; “Maw Sit Sit Vein") at Maw Sit Sit, just northwest of Namshamaw, near Kansi (Kanzi), western Kachin State, Indo-Burma Range, northern Burma.

References on maw sit sit:

Colombo, F., C. Rinaudo & C. Trossarelli. 2000. The mineralogical composition of maw-sit-sit from Myanmar. Journal of Gemmology 27(2): 87-92.

Harlow, G.E. & E.P. Olds. 1987. Observations on terrestrial ureyite and ureyitic pyroxene. American Mineralogist 72: 126-136.

Shi Guang-Hai, Jiang Neng, Liu Yan, Wang Xia, Zhang Zhi-Yu & Xu Yong-Jing. 2009. Zircon Hf isotope signature of the depleted mantle in the Myanmar jadeitite: implications for Mesozoic intra-oceanic subduction between the Eastern Indian Plate and the Burmese Platelet. Lithos 112: 342-350.

Shi G.H., B. Stockhert & Cui W.Y. 2005. Kosmochlor and chromian jadeite aggregates from teh Myanmar jadeitite area. Mineralogical Magazine 69: 1059-1075.