Maw Sit Sit: What is Maw-sit-sit?

Maw-sit-sit is a green gemstone that was named "maw-sit-sit" after the village where it was found in Northern Burma.

Since it is made of kosmochlor, chromian jadeite, chromian eckermannite, chromian albite, and other materials, maw-sit-sit is considered to be a rock, rather than a mineral. It is sometimes referred to as a variety of jadeite, but strictly speaking, maw-sit-sit is not jadeite, though it contains jadeite and is mined in the same area as imperial jadeite.

Jadeite is a mineral, whereas maw-sit-sit is a rock. The dominant mineral of maw-sit-sit is kosmochlor and this sets it apart from jadeite, which is sodium aluminum silicate. Therefore, maw-sit-sit is best considered to be related to jadeite. The kosmochlor component of maw-sit-sit is what gives it a beautiful emerald-green color with blackish-green patches.

Polished Maw sit sit

Composition

Maw sit sit is a very rare, complex, polymineralic metamorphic rock composed mainly of:

Kosmochlor – the main colouring mineral species in Maw Sit Sit is kosmochlor, a sodium chromium pyroxene previously called “ureyite”. Kosmochlor is the primary component of both the brilliant emerald-green and dark green-black patches.
Chromian Jadeite – a chromium-enriched, but still Al-dominant jadeite (Al>Cr).
Chromian eckermannite – a chromium-enriched sodium-magnesium-iron amphibole-group mineral.
Chromian albite – a chromium-enriched albite.

Mawsitsit (chromian jade) from Namshamaw Deposit,Indo-Burma Range, northern Burma.
Photo: James St. John

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.

Maw-sit-sit is also sometimes referred to as "chloromelanite" or "jade albite", which are names given to rock composed of varying amounts of jadeite, albite feldspar and other minerals.

Maw Sit Sit Age

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

Where to find maw-sit-sit

So far, maw-sit-sit has only been found in the jade mining region of Northern Burma (Myanmar) known as Tawmaw. Therefore, it is a rare rock and high quality materials command high prices.