[Rockhounds] Mineral ID

[Andrew Turner]

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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