[meteorite-list] Santa Catharina colors

[bernd.pauli at paulinet.de]

Marcin wrote:

> why shale from Santa Catharina has that many colors ?
> endpiece Wolf Creek, troilite, identical orange parts

Hello Marcin and List,

I think oxidation and alteration are the key words here:

Both Wolf Creek and Santa Catharina are extremely weathered
so the colors they display are those of extremely weathered
metallic objects. Just think of heavily corroded terrestrial,
metallic objects, which actually show the same or similar color
variations.

There is limonite, metallic parts, troilite veins and patches (nodules),
all kinds of terrestrial oxides. Oxidation has even attacked the teanite
matrix, and when these part are etched, there is sometimes excessive
blackening.

"Troilite is heavily altered to at least two different sulfides, one of which
appears to be pentlandite. In addition, free sulfur is present, often as
beautiful, yellow incrustations ... "

You do not only find sulfides but also phosphides (and copper) which
contribute to this oxidation and alteration process, but, V. Buchwald
also mentions that "the surprising problem remains, however, that it
seems to be the nickel-rich part which is the first to corrode*."

*Maybe this has something to do with Brazil's weather and climate conditions ?!


Reference:

BUCHWALD V.F. (1975) Handbook of Iron Meteorites, Volume 3, 1068-1072.


Best wishes and good night
from Germany to Poland,

Bernd