Re: Any crystallographers out there?


"Chris Hogg" <me@xxxxxxxxxxx> wrote in message
news:u52vr2d5b1rvpl2uj888hgrsp8brd77684@xxxxxxxxxx
On Tue, 30 Jan 2007 08:41:21 -0700, "WillE1" <wille1@xxxxxxxxxxxx>
wrote:


"Chris Hogg" <me@xxxxxxxxxxx> wrote in message
news:lb2ur2hcrbk1cdv2q92d046jq2up9apogq@xxxxxxxxxx
The beach near us has many granite and related pebbles on it,
including a very few with perfect or near-perfect crosses on them (I
have collected several. They derive from the Praa Sands elvan,
Cornwall, UK, if anyone's interested). My geology is sufficiently good
to know that these are twinned feldspar crystals. I also know that
feldspars twin in several systems (Carlsbad, Baveno etc.), but I don't
know and I can't find which system these perfect crosses belong to.
Can anyone enlighten me?


--
Chris

E-mail: christopher[dot]hogg[at]virgin[dot]net

Is it possible that you have Staurolite twins? If you can post an image
somewhere on the web, that would help. Will E.

No definitely not staurolite (my mineralogy's not that bad!). They are
feldspars

Chris,
When you say "crosses" I immediately think of "Chiastolite" which can either
be
either staurolite or andalusite. Twins in feldspar don't form crosses
AFAIK.
If you're invoking Cornwall granites as a source, then they could well be
Andalusite.
This may either be from the contact aureole or the granites themselves.
cheers
Bill



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Relevant Pages

  • Re: Any crystallographers out there?
    ... Cornwall, UK, if anyone's interested). ... to know that these are twinned feldspar crystals. ... know and I can't find which system these perfect crosses belong to. ... either staurolite or andalusite. ...
    (sci.geo.geology)
  • Re: Any crystallographers out there?
    ... they do not resemble either staurolite or the crossed ... inclusions in chiastolite, ... Perhaps what you describe as crosses is not what I would describe as ... How was the partial analysis done that you posted before? ...
    (sci.geo.geology)