Chromite and Its Thin Kosmochlor and Cr-Omphacite Cortex in Amphibolite from the Myanmar Jadeite Deposits
Chromite in the amphibolites of the Myanmar jadeite deposits has not been well studied. Mineralogical studies on chromite and related kosmochlor and Cr-omphacite in the amphibolite of the Myanmar jadeite deposits were conducted. Compared to the chromite in the adjacent serpentinized peridotite, the...
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| author | Yu Zhang Guanghai Shi Jiabao Wen |
| author_facet | Yu Zhang Guanghai Shi Jiabao Wen |
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| description | Chromite in the amphibolites of the Myanmar jadeite deposits has not been well studied. Mineralogical studies on chromite and related kosmochlor and Cr-omphacite in the amphibolite of the Myanmar jadeite deposits were conducted. Compared to the chromite in the adjacent serpentinized peridotite, the chromite had higher Cr<sub>2</sub>O<sub>3</sub> (45.67–54.25 wt.%) and MnO (1.82–1.90 wt.%) but lower MgO (1.00–1.96 wt.%) and Al<sub>2</sub>O<sub>3</sub> (1.05–15.09 wt.%), similar to the published chromite compositions in jadeitite. Serpentinite was derived from a highly depleted mantle peridotite. There were at least two stages of metasomatism during the transformation of serpentinite + chromite to magnesio-katophorite + chromite + thin kosmochlor (and/or Cr-omphacite cortex). The first stage was the Ca-rich metasomatism of serpentinite, resulting in sodic-calcic amphibole (magnesio-katophorite), which preceded the formation of jadeite. The second stage of Na-rich metasomatism was produced by the Na-Al-Si-rich fluids with the magnesio-katophorite + chromite (contemporaneous with the formation of jadeite). The composition of the fluid was altered by a reaction with magnesio-katophorite, increasing the Ca-Mg content and resulting in the formation of kosmochlor rich in Ca-Mg and/or peripheral Cr-omphacite. This kosmochlor–Cr-omphacite belongs to the Jd-Kos-Di ternary join, which differs from the kosmochlor–Cr-jadeite (which belongs to the Jd-Kos join in jadeitite). The formation of jadeitite with chromite + kosmochlor + Cr-jadeite occurs when large amounts of Na-Al-Si-rich fluids have wrapped the pieces of chromite-bearing amphibolite. This also explains the proverbial “moss spray green” given that amphibole (with chromite) brings out the green color in jadeitite. |
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| spelling | doaj-art-1b17297dd6b945a0a31915c22cb328622025-01-24T13:28:13ZengMDPI AGCrystals2073-43522025-01-011517910.3390/cryst15010079Chromite and Its Thin Kosmochlor and Cr-Omphacite Cortex in Amphibolite from the Myanmar Jadeite DepositsYu Zhang0Guanghai Shi1Jiabao Wen2School of Gemmology, China University of Geosciences (Beijing), Beijing 100083, ChinaSchool of Gemmology, China University of Geosciences (Beijing), Beijing 100083, ChinaSchool of Gemmology, China University of Geosciences (Beijing), Beijing 100083, ChinaChromite in the amphibolites of the Myanmar jadeite deposits has not been well studied. Mineralogical studies on chromite and related kosmochlor and Cr-omphacite in the amphibolite of the Myanmar jadeite deposits were conducted. Compared to the chromite in the adjacent serpentinized peridotite, the chromite had higher Cr<sub>2</sub>O<sub>3</sub> (45.67–54.25 wt.%) and MnO (1.82–1.90 wt.%) but lower MgO (1.00–1.96 wt.%) and Al<sub>2</sub>O<sub>3</sub> (1.05–15.09 wt.%), similar to the published chromite compositions in jadeitite. Serpentinite was derived from a highly depleted mantle peridotite. There were at least two stages of metasomatism during the transformation of serpentinite + chromite to magnesio-katophorite + chromite + thin kosmochlor (and/or Cr-omphacite cortex). The first stage was the Ca-rich metasomatism of serpentinite, resulting in sodic-calcic amphibole (magnesio-katophorite), which preceded the formation of jadeite. The second stage of Na-rich metasomatism was produced by the Na-Al-Si-rich fluids with the magnesio-katophorite + chromite (contemporaneous with the formation of jadeite). The composition of the fluid was altered by a reaction with magnesio-katophorite, increasing the Ca-Mg content and resulting in the formation of kosmochlor rich in Ca-Mg and/or peripheral Cr-omphacite. This kosmochlor–Cr-omphacite belongs to the Jd-Kos-Di ternary join, which differs from the kosmochlor–Cr-jadeite (which belongs to the Jd-Kos join in jadeitite). The formation of jadeitite with chromite + kosmochlor + Cr-jadeite occurs when large amounts of Na-Al-Si-rich fluids have wrapped the pieces of chromite-bearing amphibolite. This also explains the proverbial “moss spray green” given that amphibole (with chromite) brings out the green color in jadeitite.https://www.mdpi.com/2073-4352/15/1/79chromitekosmochloromphaciteMyanmar jadeite deposits |
| spellingShingle | Yu Zhang Guanghai Shi Jiabao Wen Chromite and Its Thin Kosmochlor and Cr-Omphacite Cortex in Amphibolite from the Myanmar Jadeite Deposits Crystals chromite kosmochlor omphacite Myanmar jadeite deposits |
| title | Chromite and Its Thin Kosmochlor and Cr-Omphacite Cortex in Amphibolite from the Myanmar Jadeite Deposits |
| title_full | Chromite and Its Thin Kosmochlor and Cr-Omphacite Cortex in Amphibolite from the Myanmar Jadeite Deposits |
| title_fullStr | Chromite and Its Thin Kosmochlor and Cr-Omphacite Cortex in Amphibolite from the Myanmar Jadeite Deposits |
| title_full_unstemmed | Chromite and Its Thin Kosmochlor and Cr-Omphacite Cortex in Amphibolite from the Myanmar Jadeite Deposits |
| title_short | Chromite and Its Thin Kosmochlor and Cr-Omphacite Cortex in Amphibolite from the Myanmar Jadeite Deposits |
| title_sort | chromite and its thin kosmochlor and cr omphacite cortex in amphibolite from the myanmar jadeite deposits |
| topic | chromite kosmochlor omphacite Myanmar jadeite deposits |
| url | https://www.mdpi.com/2073-4352/15/1/79 |
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