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Identity HelpHoskins Mine, Australia

2nd May 2017 12:29 UTCReiner Mielke Expert

http://rruff.info/doclib/am/vol80/AM80_165.pdf this paper talks about a schist but the only mineral listed that could cause a schistosity would be manganese rich chlorite. The sample I have is clearly schistose but the foliation appears to be due to an amber colored phyllosilicate of some type. Could this be the manganese rich chlorite? I have no idea what color manganese rich chlorite would be. Thank You

2nd May 2017 13:19 UTCErik Vercammen Expert

I suppose the mica norrishite https://www.mindat.org/min-2933.html would be able to cause schistosity.

2nd May 2017 13:56 UTCRalph S Bottrill 🌟 Manager

Mn-dominant chlorites can be varying shades of red, brown, green and black. Norrishites I have seen have been massive, not micaceous, but apparently can be prismatic. But the Mn minerals occur in Mn-rich chert bands and lenses and I don't recall seeing any schistose textures, just fine grained and massive.

2nd May 2017 14:51 UTCUwe Kolitsch Manager

Some Mn-bearing mica (e.g. muscovite) can also be brownish, as can bementite, ganophyllite and several other layered Mn silicates.

2nd May 2017 20:10 UTCReiner Mielke Expert

Thank you everyone.

Hello Ralph,

I'm assuming the study I linked to is comprehensive so within that framework that really only leaves manganese rich chlorite. Since you mentioned it can be brown that would fit. Strange that you didn't see any schist since it is mention numerous times in the paper.

2nd May 2017 22:56 UTCRalph S Bottrill 🌟 Manager

There is a banding which is probably mostly sedimentary, but enhanced a bit by deformation and formation of the amphiboles and chlorites. The amphiboles can give a foliation also, contributing to a schistose appearance.