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Tridymite ??

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Costas Constantinides August 12, 2017 10:26AM
Here is an image of a specimen that is etched out of calcite..The specimen comes from near the old calcite mines near Mary Kathleen Qld. Australia.It looks like a tridymite that can be seen on the tridymite page.The mineral is on diopside and associated with epidote some feldspar and what seems ordinary quartz..Could tridymite have formed in this situation..The image is the best I can do .Under magnification it is a flat clear hex.shape.

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Reiner Mielke August 12, 2017 05:26PM
You wouldn't find tridymite in such an association. My guess would be that it is albite. You don't have a complete crystal so it just looks hexagonal.
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Uwe Kolitsch August 12, 2017 08:23PM
Apatite?
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Costas Constantinides August 13, 2017 12:56AM
Thank you ,Reiner and Uwe.It is only 0.5mm in dia.I don't think it could be apatite as it was etched out using HCl..The feldspar that is associated is pink/orange. But under higher magnification there were a group of these hex. plates and also one quartz crystal that spears through the centre of the flat hex. mineral..( or the hex. plate formed around on the quartz).----
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Pavel Kartashov August 13, 2017 02:07AM
Hi Costas,
It is litle bit strange (from point of view thermodynamic considerations) to meet together simultaneously grown well formed quartz and tridymite crystals.
As Reiner wrote before, it may to be distinct generation of some feldspar (albite or microcline).
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Reiner Mielke August 13, 2017 11:52AM
"The feldspar that is associated is pink/orange" It would not be unusual to have a second generation of feldspar that is a different color.
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Uwe Kolitsch August 13, 2017 03:30PM
"etched out using HCl."
How much diluted was it?
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Douglas Schonewald August 13, 2017 04:30PM
Could it be a zeolite? Not unusual to have that association and I've found many zeolites etching out calcite. Almost looks like points of stilbite or maybe Lévyne?
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