FMF - Minerals Forum, discussion and message board

[Eduardoo]

Any hints will be greatly appreciated.

Regards,

Eduardo

[GneissWare]

Any hints about where it is from? Or its hardness? Or...?

[Eduardoo]

Unfortunately I have no information. I presume it is from Ecuador because I got it from a local collector that found his rocks all around Ecuador.

Hardness is not that easy to determine because it is very thin. Also SG is hard to measure since it is like a film on top of the rock matrix.

Regards,

Eduardo.

[Eduardoo]

Update:

This mineral is very soft, it gets scratched with the fingernail.

The streak has the same color as the mineral.

Maybe a somewhat dark selenite?

Regards,

Eduardo.

[gemlover]

How about Realgar or Cinnabar? Both are very soft sulfides.

John

[Eduardoo]

Thanks for your tips John.

The luster is definitely not adamantine or sub-metallic as my book says Cinnabar is. It can be described as resinous to greasy, which matches with Realgar.

It also gives off a strong odor when heated with the flame of a match.

So it looks you are right, Realgar is a strong candidate. I wonder if Realgar has been documented to occur in Ecuador.

Thanks again.

Regards,

Eduardo.

[gemlover]

don't burn and smell too much, realgar is ARSENIC sulfide.

Realgar is found in Peru, Bolivia, Chile and Argentina, so its presence in Ecuador would not be surprising.

john

[John S. White]

Without more information this unknown could be one of at least several hundred minerals and it makes little sense to speculate, in my opinion. However, the radial pattern suggests that it probably was in the form of a hemisphere or could have developed into a hemisphere if it were able to grow unimpeded. There is also a prominent cleavage imparting a platiness that is apparent and these two features would seem to make realgar highly unlikely. I have seen iron-bearing stilbite that looks exactly like this, but by saying this I am not ruling out hundreds of other possibilities.

[Jordi Fabre]

In my oppinion is NOT Realgar.

I agree with John:

[Eduardoo]

This I great! Every word in your comments teaches me something.

Two additional observations:

- the mineral does not dissolve in hydrochloric acid (at least not in 3 hours) as Heulandite is supposed to.

- after I scratch it, if I put a drop of water in the scratch, the mineral "drinks" the water avidly. But I guess that being thirsty is not diagnostic :-)

In another topic, I have written a template for the Power One calculator (iPad, etc) that calculates SG. it also allows you to introduce a series of taken measures and produces the mean and the minimum and maximum values of SG that give a statistical confidence of 95%.

If anyone wants the template I will be happy to e-mail it.

Regards,

Eduardo.

[Pete Modreski]

Eduardo,
I was just reviewing some of these older discussions that I missed while away on vacation.
It must be a bit frustrating, to have such an apparently distinctive-looking mineral, but not be able to identify it it positively!
Since it seems likely that perhaps it is one of the heavy-metal bearing minerals (such as perhaps realgar or orpiment) and not a zeolite, and you mentioned the smell when you heated it, you might perhaps try a little more of a careful observation of just what happens to this mineral when heated in a flame (with the cautions as noted, of course--just use a little and try not to breath the fumes, in case it does contain arsenic!). If you can heat a fragment carefully, say in a candle flame (an alcohol lamp flame would be better), and I don't know if you have something like a blowpipe--perhaps you could improvise one--its (realgar's) behavior, as described in Pough's Field Guide to Rocks and Minerals for example, should be,
"Fuses easily, melting to shiny mass, spreading and completely volatilizing with the characteristic garlic odor." You could obtain and test a fragment of the known mineral (realgar) for comparison.
A zeolite in contrast would (heulandite or stilbite), "Swells and writhes, finally fusing at ends to white droplets". If gypsum, it should be readily soluble in HOT dilute HCl.
Good luck,
Pete Modreski