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Improving Mindat.orgOrthochamosite

1st Aug 2011 02:31 UTCRalph S Bottrill 🌟 Manager

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.

1st Aug 2011 08:53 UTCMarco E. Ciriotti Manager

It was never discredited, but it corresponds to orthohexagonal modification of Brindley. So it is a polytype.

1st Aug 2011 09:47 UTCPeter Haas

There also is a wealth of chlorite varieties and synonyms that are not yet in the database.

1st Aug 2011 17:16 UTCRonald John Gyllenhammer Expert

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,

Ron

Bayliss (1975) http://rruff.geo.arizona.edu/doclib/cm/vol13/CM13_178.pdf

Bailey (1980) http://www.minsocam.org/msa/collectors_corner/arc/nomenclaturecl1.htm

1st Aug 2011 17:58 UTCDavid Von Bargen Manager

In Bayliss's book "Obsolete Mineral Names" he equates it to chamosite-1O_IIb

2nd Aug 2011 03:53 UTCRalph S Bottrill 🌟 Manager

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?

2nd Aug 2011 09:09 UTCMarco E. Ciriotti Manager

A revision of all the valid mineral species is current by IMA CNMNC.

2nd Aug 2011 12:24 UTCRalph S Bottrill 🌟 Manager

The IMAwebsite http://pubsites.uws.edu.au/ima-cnmnc/imalist.htm says the list should be updated this year.

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