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PhotosThis is an incorrect ID

23rd Sep 2019 03:49 BSTChristopher Emproto

The white mineral is most likely calcite. Cristobalite is geologically implausible for this deposit given the formation conditions. 

23rd Sep 2019 08:45 BSTAlfredo Petrov Manager

Should be easy to check with a drop of acid where that upper ball is exposed at the surface.

16th Oct 2019 16:41 BSTUwe Kolitsch Manager

Message sent.

18th Oct 2019 17:12 BSTUwe Kolitsch Manager

Kuno Stöckli replied (in German, so I translate here) as follows:

The occurrence of cristobalite in amethyst is well known, see e.g. Gübelin/J.Koivula "BILDATLAS der Einschlüsse in Edelsteinen", p. 157.
The crystal is now in the Natural History Museum in Budapest. 

Another crystal with cristobalite is shown in the above photo.

EDIT: Considering the size of these cristobalite aggregates, they will have been analysed at some time by either powder XRD or Raman spectroscopy (at least one hopes so).

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