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Where is it from?
  
  Index -> What is it? - Where is it from?
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Sante Celiberti




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PostPosted: Dec 30, 2021 17:04    Post subject: Where is it from?  

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



IMG_20211230_190602.jpg
 Mineral: Quartz
 Dimensions: 88 x 47 mm
 Description:
Mexico?
The roundish edges and tips suggest a dissolution or a pseudomorphose (after scalenohedral Calcite?).
 Viewed:  1841 Time(s)

IMG_20211230_190602.jpg



IMG_20211230_224728.jpg
 Mineral: Quartz
 Dimensions: 88 x 47 mm
 Description:
Mexico?
The base is strongly dissolved.
 Viewed:  1837 Time(s)

IMG_20211230_224728.jpg


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Jordi Fabre
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PostPosted: Feb 18, 2022 12:38    Post subject: Re: Where is it from?  

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




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PostPosted: Feb 18, 2022 14:33    Post subject: Re: Where is it from?  

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
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James Catmur
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PostPosted: Feb 18, 2022 14:39    Post subject: Re: Where is it from?  

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 wrote:
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
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Sante Celiberti




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PostPosted: Feb 18, 2022 15:15    Post subject: Re: Where is it from?  

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
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James Catmur
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PostPosted: Feb 19, 2022 03:37    Post subject: Re: Where is it from?  

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.

Sante Celiberti wrote:
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
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Jordi Fabre
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PostPosted: Feb 19, 2022 05:31    Post subject: Re: Where is it from?  

James Catmur wrote:
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.

Sante Celiberti wrote:

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


It is very characteristic of the menilite, variety of the Opal, that they present these forms due the covering of the 'diatomite' of the Opal:

https://www.mineralogia.es/index.php?searchterms=menilite&searchauthor=-&level=search

As always, it would have to be analyzed, but at first glance it seems to be that. Fluorescence is not so useful in this case because menilite in general has just a very low fluorescence in yellow with the long wave of the UV, probably by the 'diatomite' that covers them.

Sometimes formations like this are also called menilite but are actually chert. In Spain they usually have Opal in the central nodule but in other places, sometimes not and they are just chert.
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Bob Morgan




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PostPosted: Feb 19, 2022 14:25    Post subject: Re: Where is it from?  

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.
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Sante Celiberti




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PostPosted: Feb 20, 2022 17:02    Post subject: Re: Where is it from?  

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



IMG_20220220_185149.jpg
 Description:
Quartz pseudomorphic after Calcite (?)
Mexico (?)
88 x 47 mm
 Viewed:  1145 Time(s)

IMG_20220220_185149.jpg



IMG_20220220_185242.jpg
 Description:
 Viewed:  1145 Time(s)

IMG_20220220_185242.jpg



IMG_20220220_192229.jpg
 Description:
 Viewed:  1144 Time(s)

IMG_20220220_192229.jpg



IMG_20220220_185551.jpg
 Description:
 Viewed:  1145 Time(s)

IMG_20220220_185551.jpg



IMG_20220220_190825.jpg
 Description:
 Viewed:  1145 Time(s)

IMG_20220220_190825.jpg



IMG_20220220_190040.jpg
 Description:
 Viewed:  1145 Time(s)

IMG_20220220_190040.jpg



IMG_20220220_190110.jpg
 Description:
 Viewed:  1145 Time(s)

IMG_20220220_190110.jpg



IMG_20220220_194910.jpg
 Description:
Zenithal view.
 Viewed:  1143 Time(s)

IMG_20220220_194910.jpg



IMG_20220220_192338.jpg
 Description:
Detail of the surface.
 Viewed:  1145 Time(s)

IMG_20220220_192338.jpg


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James Catmur
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PostPosted: Feb 21, 2022 03:37    Post subject: Re: Where is it from?  

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




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PostPosted: Feb 21, 2022 14:38    Post subject: Re: Where is it from?  

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

Thanks again.
Sante
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Bob Morgan




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PostPosted: Feb 27, 2022 17:32    Post subject: Re: Where is it from?  

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.
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