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Posted by Ralph Bottrill  
avatar Orthochamosite
August 01, 2011 01:31AM
Cleaning up chlorites on Mindat, I see this species is listed as "Discredited 1975", and described as a polytype of chamosite (probably true) but I can find no reference to this discreditation. It is listed as Grandfathered on the IMA list by Nickel and Nichols (2008). Bayliss lists it in this 2000 glossary of discredited names, but I dont have access to this. Its not listed in the latest Dana, but is in most other recent lists. Any information would be welcome.

avatar Re: Orthochamosite
August 01, 2011 07:53AM
It was never discredited, but it corresponds to orthohexagonal modification of Brindley. So it is a polytype.
avatar Re: Orthochamosite
August 01, 2011 08:47AM
There also is a wealth of chlorite varieties and synonyms that are not yet in the database.
avatar Re: Orthochamosite
August 01, 2011 04:16PM
Hi Ralph,

Rather than an actual discreditation, it was more like "discreditation by omission." Bayliss simply recommended Chlorite names which did not include Orthochamosite, in fact calling it a variety that should be discarded and so stating, " The varietal names of brunsvigite, corundophilite, daphnite, delessite, diabantite, grovesite, kiimmererite, kotchubeite, leuchtenbergite, orthochamosite, pennine, pseudothuringite, pycnochlorite, ripidolite, sheridanite, talc-chlorite and thuringite should be discarded. The varieties between these end-member compositions should be described by chemical element adjectives. At present the polytype symbols of Brown & Bailey (Amer. Mineral. 47, 819) should be used"

Ideal end member examples:

Dioctahedral chlorite: Donbassite
Di,trioctahedral chlorite: Cookeite (Li-rich), sudoite (Li-poor)
Trioctahedral chlorite: Clinochlore (Mg), chamosite (Fe2+), nimite (Ni), pennantite (Mn2+), baileychlore (Zn); as dominant end members

*Special case- trioctahedral 2:1 layer with dioctahedral interlayer: Franklinfurnaceite

As Marco says, Orthochamosite is considered an orthohexagonal modification.

Hope this helps,

Bayliss (1975) [rruff.geo.arizona.edu]
Bailey (1980) [www.minsocam.org]
avatar Re: Orthochamosite
August 01, 2011 04:58PM
In Bayliss's book "Obsolete Mineral Names" he equates it to chamosite-1OIIb
avatar Re: Orthochamosite
August 02, 2011 02:53AM
So it seems we all agree its just a polytype, but I guess we need to retain it as a species until the IMA gives it the boot. Maybe no-one wants to be on a chlorite subcommittee?

avatar Re: Orthochamosite
August 02, 2011 08:09AM
A revision of all the valid mineral species is current by IMA CNMNC.
avatar Re: Orthochamosite
August 02, 2011 11:24AM
The IMAwebsite [pubsites.uws.edu.au] says the list should be updated this year.



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