[Rockhounds] Lepidolite

[Jeanette Wimpee]

Well, that answered an unasked question of mine.
I have some pink lepidolite with reddish purple "spots" distibuted 
throughout, similar to ruby in zoisite. I had been wondering if the darker 
colored spots were something other than lepidolite.
See, if you hang around long enough even the questions you don't ask will 
get answered by the wonderful rockhound listers.
Jeanette





> The lithium mica (e.g. lepidolite) phase diagram has something like 17 
> separate end members (I used it as a cover for a paper I did in phase 
> equilibria class).  This means that there is technically some 17 different 
> dimensions to the diagram, good luck on the visualization and modelling. 
> It takes very little changes in temp., pressure, or chemsitry while the 
> mineral is forming to cause lithium (or any) mica to have a different 
> color and/or slightly varying chemisty, even to make it a separate 
> species. This is common for many pegmatite minerals due to how they form 
> and how many of them are "trash can" minerals in that they can accept 
> numerous different elements into their structures (check out the 
> tourmaline or the ferrocolumbite-manganotantalite series.  Yellow, purple, 
> and pink lepidolite can be found together.  I even have some pieces from 
> South Dakota that are half biotite and half muscovite (a small reaction 
> zone of possible phlogopite is seen at the contact).  Hope this helps.
>
> Andrew Turner
> Victorville, CA USA
>
>
>>From: "Lawrence Rush" <larryrush at worldnet.att.net>
>>Reply-To: "Rockhounds at drizzle.com: A mailing list for rock and gem 
>>collectors"<rockhounds at lists.drizzle.com>
>>To: "Rockhounds at drizzle.com: A mailing list for rock and gem 
>>collectors"<rockhounds at lists.drizzle.com>
>>Subject: Re: [Rockhounds] Mineral ID
>>Date: Fri, 7 Mar 2008 16:45:22 -0500
>>
>>While I am asking questions about the micas, let me try another one....
>>
>>I recently got some "bi-colored" Lepidolite from Brazil, so- called 
>>because it has a darker colored purple "rind" covering the sides of the 
>>primary crystal faces, but still part of the crystallographic structure. 
>>The line of demarcation between the 2 colors is distinct. My question is: 
>>Would this likely be due to a change in the chemistry (or pressure, 
>>temperature, etc.) of the melt while crystallization occurred or is it an 
>>alteration that happened post crystallization?
>>
>>Just curious......Larry
>>
>>
>>>Subject: [Rockhounds] Mineral ID
>>>
>>>
>>>
>>>Does anyone know the mineral species associated with the following
>>>aluminosilicate oxyfluorides? I have no reference work in which to find 
>>>these.
>>>
>>>The numbers following the formulas are the crystallographic pdf numbers
>>>..................
>>>
>>>NaMg3AlSi3O10F2 - 25-0842
>>>BaMg3Al2Si2O10F2  - 19-0117
>>>
>>>
>>>
>>>Thanks......Larry Rush
>>>
>>>"Noel Coward thought work was more fun than play,  but he never, ever 
>>>worked in
>>>the mines"
>>>
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