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[Sante Celiberti]

Hello.

I've lost the label of this specimen.
I vaguely remember it is from Mexico, but I could be wrong.
Can anyone help me with the exact locality and any other information about this Quartz?
Thanks in advance.

I wish all the friends of the Forum a happy new year.
Sante

[Jordi Fabre]

No idea Sante, sorry. Is not easy due the similitude of the Opals from different localities.

[Sante Celiberti]

Thank you so much, Mr. Jordi.

I'm confused why you call into question the Opal.
Is it a miswriting or do you know a pseudomorph Opal with such a shape?
If so, I would be interested to know more about it.

Best regards.
Sante

[James Catmur]

The problem is that you can find opal like this in so many places in the world. So it is impossible to know where it was found

[Sante Celiberti]

Hi, James.

Are Jordi and you meaning my specimen is a pseudomorph Opal (and not a Quartz)?
Sorry, I was not aware of it.
Now I understand why my research has so far been unsuccessful.

Thanks and greetings.
Sante

[James Catmur]

Have you tested the hardness? That will help you determine if it is opal or some other mineral. Based on the photo I could believe it to be opal, but have no idea where it is from.

[Jordi Fabre]

[Bob Morgan]

I take your word for it being quartz. Such casts are common in many localities with only partial dissolution of the calcite. I have one cast from Santa Eulalia, but it is reddish. Over the years I have seen many quartz overcoats of several minerals from Mexico.
If the surface could be better seen in a photo, that might help.
If Peter Megaw has recovered from the Tucson show, perhaps he could have some helpful leads.

[Sante Celiberti]

Hello, Jordi, James and Bob.
Thank you so much for your kind suggestions.

I know that such a common species doesn't deserve much attention and I'm sorry to take advantage of your time. But let's take it as a mineral recognition exercise.

The bad quality of my photos may have caused some confusion.

Of course, after more than 50 years of collecting I know the so-called "Opal-menilite" and I exclude that my specimen is that.
Despite the rounded shapes, many faces and edges are clearly recognizable, and this excludes that it is an Opal, unless it is a pseudomorphic Opal.
But the piece scratches the glass and this definitively excludes that it could be an Opal.

Hardness 6 suggests Quartz.

If it were a primary Quartz the possible dissolution would have produced an ambiguous shape, close to a bi-terminated Tessin Quartz or scalenohedral Calcite.
A bi-terminated Tessin Quartz, with such a strong white color, would be very interesting and attractive, but I've never seen one...

The hypothesis of pseudomorphic Quartz after scalenohedral Calcite, the latter so well represented in Mexico (where the piece possibly comes from), seems very probable.

Let's hope for some kind help from the Mexican expert Peter Megaw.

Best regards.
Sante

[James Catmur]

The new photos help. The hardness does too. Could it be a quartz epimorph / cast?

[Sante Celiberti]

Sorry, James.
No reaction to hydrochloric acid.
I would say complete pseudomorphosis.

Thanks again.
Sante

[Bob Morgan]

Have you tried the acid all over the bottom of the specimen? If Calcite is inside there is probably some access to it that will produce bubbling. I'm assuming it is not hollow inside.
The coating is not what I've usually seen on an overgrowth by quartz. It's usually more distinct small crystals. It reminds me of the coating over quartz crystals in Keokuk geodes.