FMF - Friends of Minerals Forum, discussion and message board

[lluis]

Dear List

I recently got a small piece of rhodochrosite from N´Chwaning that has has the shape of a dodecahedrom.
I tried to consult in Atlas Mineralienformen but I could not find rhodos there.

I was told that those appeared in Tucson several years ago.

Trouble for me is that I could not imagine that a romboedric crystal could mimic a cubic crystal and I am begining to try to find out if it is really a odd rhodo or just another mineral...

May the wiser listmembers let me know theirs valued opinions?

With best wishes

Lluís

[crocoite]

A photo would help Lluís...

[Matt_Zukowski]

Rhodochrosite will not form true dodecahedrons. Carbonates, like many minerals, can form xtals that look like they come from a different xtal class, but they do not form true xtals from other xtal classes. Look closely at the interface angles - I'll bet they do not correspond to a dodecahedron.

[lluis]

Hi, crocoite, Matt

Well, Matt, as far as I see they are rhombs, and there are 12 faces.

When I got it and examined, I would bet for a garnet from Sierra de las Cruces (those pink ones, just small), or a pink garnet from Jeffrey Mine.

I saw some bevelled rombohedrons of Rhodo, but they have not 12 faces.

And yes, agreed completely that if cubic could not be a rhodo.
But seller was so sure that it is a rhodo, adding that they appeared in Tucson some years ago, that.... i bought to be able to see in in the flesh

Any opinion, or if any list member have seen those poieces in Tucson, would be great

With best wishes

Lluís

[Pete Richards]

The photo, while small, certainly seems to show a dodecahedron. And the color is not right for rhodochrosite, but is appropriate for garnets, which do occur at N'Chwaning. I just bought several hematite specimens from N'Chwaning #2 which include small garnets of about that color. Don't know if they are grossular or a different garnet species.

If you are feeling adventurous, put the specimen briefly in some dilute hydrochloric acid. If it fizzes slowly it is (or was) rhodochrosite. I predict that it will not fizz, and will not be harmed in any way by the acid.

While the crystal is small, it is big enough that you should also be able to test its hardness. Garnet is much harder than rhodochrosite. Garnet will not be scratched by a knife or steel pin, but rhodochrosite will be.

[crocoite]

You are right Lluis, it does look like a garnet. Be interesting to see the results of Pete's test.

Regards
Steve

[lluis]

Good evening, Pete, crocoite

Well, I am (and I was) pretty sure that it is garnet, simply that maybe it could be another cubic species
Colour in person is a red like that of Uchucchaqua rhodos, so, colour could match to a rhodo.
What does not match is a cubic simmetry in a rhombic compound...
For a garnet in N'Chwaning, I have always seen deeper in colour, but if you have seen a pinkish one, well, at least locality seems that is correct.... (hurrah! :-( )

Anyway, another piece for my black cabinet....Bought from same seller that was selling the "palladian golds"... Even after I said him they were fake, following the results of Cesar.

Ughhhhh!
Did I say why I rely in very few sellers?
That buying was just "I would like to see it in person". I did also buy an aluminum denarius (woooowwww! romans were very advanced! they did electrolysis to get aluminum! :-) ) adverted as "odd limes", along with a tin silver plated denarius (also, adverted and insisted when I said tin, as limes. A late 1800's pice. Very "roman", of course :-( )
Curiosity killed the cat, but he return to live for satisfaction to have satisfied his curiosity.... :-)

With best wishes

Lluís

P.D.: Jordi, I coud never be enough grateful to you for the anlaysis you provide!