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Robson Vieira
Joined: 05 Jan 2017
Posts: 41
Location: São Paulo
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 Posted: Jul 28, 2024 15:54 Post subject: Altered quartz or pseudomorph? |
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Hi,
I collected this sample in an ignimbrite quarry. As you can see it is an agglomerate of non-crystalized quartz, but I wonder the sample is crystalized itself, because the stuff seems a sandstone blank. No, there are not any hexagonal crystal appearance, nor hexagonal faces. I provide a pic with lines of the correct angles and faces in order to help visualization.
Please, note the two semi crystals on the lateral faces of the crystal, they have the same structure of it.
Could it be a pseudomorph? Quartz after what? Since the crystal shape of the sample is quite different from the usual for a quartz, I ask you all help.
Thanks
| Mineral: | Quartz |
| Locality: | | Paraná, Brazil |  |
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| Dimensions: | 3,5 cm x 4,5 cm |
| Description: |
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| Viewed: |
1506 Time(s) |
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| Mineral: | Quartz |
| Locality: | | Paraná, Brazil | |
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| Dimensions: | 3,5 cm x 4,5 cm |
| Description: |
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| Viewed: |
1506 Time(s) |
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| Mineral: | Quartz |
| Locality: | | Paraná, Brazil | |
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| Dimensions: | 3,5 cm x 4,5 cm |
| Description: |
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| Viewed: |
1503 Time(s) |
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| Dimensions: | 3,5 cm x 4,5 cm |
| Description: |
| Angles between the faces seen from above |
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| Viewed: |
1505 Time(s) |
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| Mineral: | Quartz |
| Locality: | | Paraná, Brazil | |
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| Dimensions: | 3,5 cm x 4,5 cm |
| Description: |
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| Viewed: |
1508 Time(s) |
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James Catmur
Site Admin
Joined: 14 Sep 2006
Posts: 1381
Location: Cambridge
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| Posted: Jul 29, 2024 08:08 Post subject: Re: Altered quartz or pseudomorph? |
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| It could be an epimorph (where one mineral coats another one) of a cubic mineral
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Bob Morgan
Joined: 18 Jan 2018
Posts: 233
Location: Savannah, Georgia
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| Posted: Jul 29, 2024 10:11 Post subject: Re: Altered quartz or pseudomorph? |
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| This may be a sand crystal, perhaps of feldspar.
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Robson Vieira
Joined: 05 Jan 2017
Posts: 41
Location: São Paulo
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| Posted: Jul 29, 2024 14:34 Post subject: Re: Altered quartz or pseudomorph? |
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| James Catmur wrote: | | It could be an epimorph (where one mineral coats another one) of a cubic mineral |
Thanks your guess. Any tip to figure out the cubic one?
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Robson Vieira
Joined: 05 Jan 2017
Posts: 41
Location: São Paulo
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| Posted: Jul 29, 2024 14:36 Post subject: Re: Altered quartz or pseudomorph? |
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| Bob Morgan wrote: | | This may be a sand crystal, perhaps of feldspar. |
Do you mean a feldspar with quartz granular content? A Sandy feldspar?
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Bob Carnein
Joined: 22 Aug 2013
Posts: 337
Location: Florissant, CO
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| Posted: Jul 29, 2024 14:48 Post subject: Re: Altered quartz or pseudomorph? |
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| I'm having trouble seeing the angles you've measured on the pictures. In the second photo, the sample looks like a hexagonal prism with one side broken and a combination of a hexagonal prism and a basal pinacoid. That suggests a perimorph or incrustation pseudomorph. This seems like a very odd occurrence in an ignimbrite.
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Bob Morgan
Joined: 18 Jan 2018
Posts: 233
Location: Savannah, Georgia
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| Posted: Jul 30, 2024 08:11 Post subject: Re: Altered quartz or pseudomorph? |
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I was wrong to suggest feldspar. I know of no instance of feldspar sand crystals.
What you have could be a pseudo cubic quartz sand crystal.
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Riccardo Modanesi
Joined: 07 Nov 2011
Posts: 623
Location: Milano
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| Posted: Jul 30, 2024 08:23 Post subject: Re: Altered quartz or pseudomorph? |
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Hi to everybody!
I don't fell like excluding another one which wasn't mentioned yet by anybody here: FLUORITE! It's not so seldom to find it as a covering mineral on quartz crystals!
Greetings from Italy by Riccardo.
_________________
Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo. |
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