16.49: Maw-sit-sit
- Page ID
- 4736
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|---|---|
| Chemical composition | Chromium bearing rock |
| Hardness | 6-7 |
| Fracture | Irregular to conchoidal |
| Refractive index | 1.52 (common) - 1.74 |
| Specific gravity | 2.5-3.5 |
| Lustre | Vitreous to oily |
Figure \(\PageIndex{1}\): Cabochons of Maw Sit Sit
| Maw-sit-sit image gallery |
Maw-sit-sit is a chromium-rich metamorphic rock with brilliant emerald green blotches and bands interspersed with dark green-black blotches. It is found in Tawmaw, Myitkyina-Mogaung District, Kachin State, Myanmar.
It was first noted in the early 1960’s by the famed Swiss gemologist Eduard J. Gübelin during field investigations in Burma. The locality is near the historic imperial jadeite mines of northern Myanmar.
Synonyms: mawsitsit, maw-sit-sit jade, chrome-jade, kosmochlore-jade, chrome-albite, jade-albite, chloromelanite.
Chemical composition
Most of the component minerals of mawsitsit contain chromium as either an essential element or as an impurity. The proportions of each component mineral can vary from example to example.
- Kosmochlor – the dominant mineral species in mawsitsit is kosmochlor, a sodium chromium pyroxene previously called “ureyite”. (Ureyite was discredited as a mineral species when it was determined to be identical to kosmochlor.) Kosmochlor constitutes about 60 percent of mawsitsit, and is the primary component of both the brilliant emerald green and dark green-black patches.
- Chromian Jadeite – a chromium-enriched jadeite makes up approximately 15 percent of mawsitsit.
- Chromian Eckermannite – a chromium-enriched sodium, magnesium, iron amphibole group mineral, makes a small contribution of only about 4 percent of mawsitsit.
- Chromian Albite – a chromium-enriched albite usual constitutes 1 per cent of mawsitsit.
- “Symplectite” – On several occasions, derivative descriptions of the mineralogy of mawsitsit includes “symplektite” (symplectite) in the list of the mineral species present. Symplectite is not a mineral but rather a petrographic texture, a microscopically-fine intergrowth of two or more minerals resulting from high-pressure metamorphism.
- Minor and trace minerals include chromite (usually as opaque, microscopic relict grains), natrolite, an imprecisely identified chlorite-group mineral and an imprecisely identified serpentine-group mineral.
Diagnostics
Color
Brilliant emerald green to dark green, almost black. Patterning varies from splotches to swirls to veins and bands.
Diaphaneity
Opaque; very slightly translucent in thin splinters.
Refractive Index
The refractive index has been given as varying between 1.52 (most common) and 1.74. The refractive indices for the two dominant minerals present in maw-sit-sit are:
- Kosmochlor: biaxial, nα = 1.766, nγ = 1.781, birefringence = 0.0150
- Jadeite: biaxial (+), nα = 1.654-1.673, nβ = 1.659-1.679, nγ = 1.667-1.693, birefringence = 0.0130-0.0200
Occurrence
Maw-sit-sit was the result of high pressure, low temperature metamorphism of a chromium-rich ultramafic rock. It occurs on the rim of a peridotite intrusion that has been altered to serpentine. To date, the occurrence in northern Myanmar appears to be unique. A mixture of kosmochlore with eckermannite has been noted in Japan, but bears no resemblance to mawsitsit.
Care
It has been suggested that maw-sit-sit not be cleaned using ultrasonic cleaners or chemical cleaning agents, nor should it be exposed to rapid fluctuations in temperature.
Sources
- Hänni, H.A. & Meyer, J. (1984): Is there a gap in the solid solution between jadeite and Ureyite? (German original title: Besteht eine Mischungslücke in der Reihe Jadeit-Ureyit). Paper verbally presented at Bern-Basel Colloquium in Bern.
- Chiu Mei Ou Yang. 1984. A terrestrial source of ureyite. American Mineralogist, Vol. 69, pp 1180-1183
- Colombo, F., C. Rinaudo and C. Trossarelli. 2000. The mineralogical composition of maw-sit-sit from Myanmar. Journal of Gemmology. Vol. 27 No.2: pp 87-92
- Gübelin E.J. (1964–65) Maw-sit-sit: A new decorative gemstone from Burma. Gems & Gemology, Vol. 11, No. 8, pp. 227–238, 255
- Gübelin E.J. (1965b) Maw-sit-sit–A new decorative gemstone from Burma. Journal of Gemmology, Vol. 9, No. 10, pp. 329–344
- Gübelin E.J. (1965c) Maw-sit-sit proves to be jade-albite. Journal of Gemmology, Vol. 9, No. 11, pp. 372–379
- Hänni H.A., Meyer J. (1997) Maw-sit-sit (kosmochlore jade): A metamorphic rock with a complex composition from Myanmar (Burma). Proceedings of the 26th International Gemmological Conference, Idar-Oberstein, Germany, pp. 22–24
- Htein, W. and A.M. Naing. 1995. Studies on kosmochlor, jadeite and associated minerals in jade of Myanmar. Journal of Gemmology. Vol. 24, pp.315-320
- Qi, L., X. Lu, W. Liu and Q.Ouyang. 2003. Maw-sit-sit jade from Burma: A particular jade formed by dynamic metamorphism and metasomatism. Journal of Gems and Gemmology. Vol. 5 No. 4, pp.1-7
Additional notes
Prof. Hänni added the following to the sources entry:
"I would like to add an early reference on Maw-sit-sit analysis, the data were presented verbally in Bern in Spring 1984. The research was done on thin sections, using optical and microprobe methods. The in those days new and striking results were presented at a colloquium hold every year between the mineralogical institutes of Basel and Bern, Switzerland. Hänni and Meyer have already gone a long way to finish a publication when the paper of Ou Yang appeared in later 1984. There was all power lost to finish and publish almost the same as the findings of Ou Yang showed. Hänni came back to the topic in an International Gemmological Conference IGC in Idar Oberstein 1997 much to the amusement of Ms Ou Yang, who was in the audience."
[ed.: source now mentioned]