Atacamite

'Paratacamite' is not in the list of the polymorphs.

And correctly so.

Although long considered as the rhombohedral polymorph of Atacamite, Paratacamite has been recently shown to contain essential Zinc, in part replacing Copper in one position and helping stabilize the trigonal cell. This prevents it from being a polymorph of Atacamite. In this context, it's the Cu-dominant analogue of Herbertsmithite, Haydeeite and Gillardite.

Lefteris.

Lefteris,

Best wishes for 2012, and thanks for the info. It should be put on the atacamite page also, for this is new and a lot of amateurs like myself may have the same reaction about paratacamite being 'forgotten'.



Edited 1 time(s). Last edit at 12/27/2011 11:22AM by Erik Vercammen.

Does Atacamite contain any Zn? If so what would be the maximum it could contain?

Reiner - I don't know, I'm also one of the amateurs here.

If I remember correctly, it was Uwe Kolitsch that brought up the matter of Zn content in Paratacamite in a discussion some time ago, before the mindat page was updated. Maybe he would know.

However, I believe that the discovery and description of several new species in the Atacamite group recently, has brought some changes in the understanding of the crystal chemistry and structures within the group.

Lefteris.

The reason I am asking is that I was wondering if semi-quantitative EDS would be useful for distinguishing Atacamite from Paratacamite. That would only work if Atacamite did not contain much Zn compared to paratacamite.

Well, since Zn is essential in Paratacamite, no Zn at all would indicate Atacamite - especially if coupled with an orthorhombic xl form.

Lefteris.

The name Atacamite does not come from Dimitri Golytsin in his ‘Recueil des noms par ordre alphabetique apropries en Minéralogie’, as stated in most sources, but stems from the german naturalist Johann Friedrich Blumenbach (1752 - 1840), who described and named it in his work 'Handbuch der Naturgeschichte, fünfte Auflage 1797 S. 660.'

[books.google.be]