FMF - Friends of Minerals Forum, discussion and message board

[Montanpark]

Dear all,
very interesting thread as those pseudomorphs have interested me since a long time. I remember that i saw the first one during my student times at the Aachen University mineral collection where a quite large totally (at least visually) copper replaced "aragonite" was on display in the pseudomorph case (and it seemed to be a quite old one).

Almost 2 decades later i was lucky to acquire quite a lot of those and there were different stages of replacement from fully replaced to only skeletal like replacement with lot of carbonate left. I intentionally say carbonate as i have never tested if it was aragonite or calcite paramorphosing twinned aragonite. I performed some tests by carefully etching some specimens and very interesting structures were revealed, one of them Frank de Wit has seen recently when visiting me, you may remember that small specimen, Frank.

Last year when i visited the Krantz store in Bonn i found a few - 2 or 3 - samples labeled copper after aragonite and i purchased them - to see later (they were dusted from decades) that there was obviously no copper, just carbonate. If anybody wants to perform analyses on a sample i´ll be glad to send one of those, as i won´t have the time for quite a while now. Just leave me a message.

And Alfredo, ya know i like your sense of humour ;-)

Cheers
Roger

[Carles Curto]

I add a PDF page of Kempf, O., Tawackoli, S., Para, W.H. 2003. Minerales de Bolivia. Minera San Cristobal, S.A. 121+16 pp. La Paz.

[Carles Curto]

And more (from: Salomón Alivas, V., Ahlfeld, F. 1998. Los minerales de Bolivia y sus parajes. Tomo I. 326 pp. Santa Cruz de la Sierra - Bolivia.

Textual, pg. 295: (Aragonito) "Bien conocido son los cristales de aragonita en las arcillas rojas de los "Ramos" de Corocoro, principalmente en las minas de San Agustín y Malcocoya. Tienen hasta 3 cm. de diámetro y se presentan en maclas cíclicas de tres individuos, de contornos hexagonales.
A veces están parcialmente o enteramente substituídos por cobre nativo".

And, more or less translated to english: The crystals of aragonite are well known in red clays at "Los Ramos" in Corocoro, mainly in San Agustín and Malcocoya mines. They reach 3 cm on diameter and form cyclic twins (of hexagonal contour) of three individuals.
In some cases they are partially or completely substituted by native copper.