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Improving Mindat.orgGarnets and Pyroxenes from Huanggang Mine, Inner Mongolia
15th Aug 2012 15:00 UTCPeter Haas
Free pdf (note that this server is very slow and may be unresponsive during daytime in China):
http://www.yskw.ac.cn/ch/reader/create_pdf.aspx?file_no=201101009&flag=1&journal_id=yskwxzz
From analyses of skarn mineral compositions in a large number of samples (analytical results included), this paper comes to the following results:
Garnets:
Composition varies from andradite (Adr 28.69-96.44) to grossular (Grs 2.00-67.38). Garnets formed at an early stage are andradites of nearly end-member composition, while garnets formed in the major ore-forming stage are grossulars. Grossular is also dominant in retrograde skarn assemblages.
Pyroxenes:
Composition varies from diopside (Di 11.80-94.12) to hedenbergite (Hd 4.08-81.28). Pyroxenes formed at an early stage are diopsides, while pyroxenes formed in the major ore-forming stage are hedenbergites.
Conclusions:
- It is very unlikely that all garnet specimens traded from Huanggang Mine are andradites. I assume that they are notoriously labelled as such without having ever been analyzed.
- Combinations of andradite with diopside or grossular with hedenbergite are common, while those of andradite with hedenbergite or grossular with diopside are very unlikely to occur. Again, the mindat gallery of Huanggang Mine grossly contradicts any scientific evidence here.
Measures:
(1) I will sent messages.
(2) All specimens of supposed andradite and/or hedenbergite should be listed as garnet and/or pyroxene until analyses can be provided that confirm their true identity.
15th Aug 2012 23:52 UTCJosé Zendrera 🌟 Manager
Yesterday I received a message from a Mindat supervisor warning me that the species could be wrong and sent a link to this post.
After reading this and the abstract of the link, and take a look to my piece, I am convinced that will be better to change the label to Andradite-Grossular series. As said, my specimen is slightly magnetic, wich suggest some Fe in the composition, also have associated diopside as generally exists in Huanggang Andradites, but as I can not know if Andradite is majority it is better to be cautious.
Peter, thanks for the information and for helping to keep Mindat a reliable site.
Andradite-Grossular series garnet cluster with associated diopside.
Huanggang Mine, Hexigten Banner (Keshiketeng Co.), Ulanhad League (Chifeng Prefecture), Inner Mongolia Autonomous Region, China
Overall size: 5,2 x 4 x 3,5 cm
16th Aug 2012 01:39 UTCPeter Haas
The composition change from andradite to grossular (and diopside to hedenbergite) from early to late mineralization stages suggests that the zoned garnets have a higher andradite component in the core and grade outwards to higher grossular components. Specimens with a second generation of greenish/orangish yellow crystals overgrowing earlier dark brown crystals are likely grossular on andradite (but this still needs to be confirmed by analysis).
16th Aug 2012 14:49 UTCJosé Zendrera 🌟 Manager
http://www.foro-minerales.com/forum/viewtopic.php?p=77895#77895
These neodimium magnets are very strong!
Almandine-Spessartine series garnet
Shigar Valley, Skardu District, Baltistan, Gilgit-Baltistan (Northern Areas), Pakistan
5 x 4,5 x 3 cm. 118 g.
17th Aug 2012 11:05 UTCRock Currier Expert
17th Aug 2012 11:29 UTCPeter Haas
EDIT:
I have added a comment to the locality page. Otherwise, I only wonder why people apparently don't learn their lessons and still strongly believe in labels. Remember the many Yaogangxian specimens that have been proven to be mislabelled ...
26th Aug 2012 17:03 UTCNik Nikiforou
In my experience, the Huanggang Mine garnets are not themselves magnetic; I believe that the matrix on some specimens is rich in magnetite. I acquired a large lot of these at the Tucson show and I detect no magnetism in the garnet crystals themselves, but a strong magnetism on pieces with matrix. In some cases I could get my neodymium magnet to adhere loosely to a garnet crystal, but only if there was a significant amount of matrix just beneath it.
I'd be curious to know if that is also the case with your specimens.
Nik Nikiforou
"Sometimes being smart is just dumb luck"
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Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 19, 2024 20:32:52