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Datolite locality question
  
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Mathias




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PostPosted: Jul 31, 2022 06:18    Post subject: Datolite locality question  

Dear FMF specialists,

I've just acquired a small batch of mineral specimens, 10 pcs, half of them are from Peru, containing Tetrahedrite, Galena sphalerite, Rhodochrosite in various combinations.
But there was also a relatively large specimen supposedly Datolite among this batch. It however came without a label (alike the other 9 specimens but these are easily determinable regarding locality), meaning that I basically know nothing about it.

Besides colorless Datolite crystals, there is a small amount of another purple-colored mineral present. The backside of the specimen is completely filled with small Datolite crystals.

Is there anybody out there who has a clue where this specimen might be from?

Thanks and regards,
Mathias



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 Mineral: Datolite
 Dimensions: 12 * 8 * 4 (cm)
 Description:
 Viewed:  1910 Time(s)

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 Description:
 Viewed:  1915 Time(s)

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 Description:
 Viewed:  1910 Time(s)

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DSC07540.JPG
 Description:
 Viewed:  1900 Time(s)

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DSC07532.JPG
 Description:
 Viewed:  1900 Time(s)

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Kevin Schofield




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PostPosted: Jul 31, 2022 11:53    Post subject: Re: Datolite locality question  

Mathias wrote:
Dear FMF specialists,

I've just acquired a small batch of mineral specimens, 10 pcs, half of them are from Peru, containing Tetrahedrite, Galena sphalerite, Rhodochrosite in various combinations.
But there was also a relatively large specimen supposedly Datolite among this batch. It however came without a label (alike the other 9 specimens but these are easily determinable regarding locality), meaning that I basically know nothing about it.

Besides colorless Datolite crystals, there is a small amount of another purple-colored mineral present. The backside of the specimen is completely filled with small Datolite crystals.

Is there anybody out there who has a clue where this specimen might be from?

Thanks and regards,

Mathias


Hi Mathias,

I don't think I can be much help on the locality, but I think I can identify some of associated minerals, particularly on the rear of the piece thanks to your pretty good pictures.

In the second picture, I think that the pale yellow equant crystals to the right of the purple mineral are apophyllite
Also in the second, I suspect your purple mineral is amethystine quartz, although poorly crystallized
Several of the pictures show white/colourless scalenohedra, which I think are calcite.

All of these are, unfortunately, common associates of datolite, so not much help in narrowing down a locality, although if put to the rack, my first thought would be Charcas, Mexico, from whence (per mindat) all of these mineral are associated with the datolites

Cheers,

Kevin

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Peter Megaw
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PostPosted: Jul 31, 2022 12:20    Post subject: Re: Datolite locality question  

I agree with Kevin's calls on the associated species (I suspect the calcite is orange-pink fluorescent, which unfortunately doesn't narrow things down either). However, neither the habit nor the color of the datolite look like things I've seen from Charcas, and that DT scalenohedral calcite is uncommon from there as well.
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kushmeja




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PostPosted: Jul 31, 2022 12:25    Post subject: Re: Datolite locality question  

Looks like Prospect Park Quarry in New Jersey, USA, or possibly one of the other NJ trap rock quarries. Datolite of similar appearance is found there, and with the same associated minerals too. I have at least 1 piece at home from Prospect Park that has nearly identical Datolite crystals as far as size, color & shape. I'm out of town the next few days, or I'd post a pic now. If you check Mindat though, there should be ample examples on there too.
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Mathias




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PostPosted: Jul 31, 2022 12:38    Post subject: Re: Datolite locality question  

Dear Kevin thanks for your reply.

Could it perhaps be that the biger crystals, on the first photo, aren't datolite at all, but Calcite? I have some greenish USA (upper new street quarry)- and also Dalnegorsk Datolites in my collection but its difficult for me to compare these with the subject specimen and tell its the same crystallization, lustre, etc. just by the bare eye.

It could easily be tested with some hydrochloric acid, but I try to postpone the destructive analysis a little bit.

Thanks,
Mathias
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Peter Megaw
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PostPosted: Jul 31, 2022 12:49    Post subject: Re: Datolite locality question  

I wondered that too...UV would tell too and it's nondestructive. Datolite is also harder (5+ vs 3) so a well placed pin will tell you a lot
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Kevin Schofield




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PostPosted: Jul 31, 2022 13:13    Post subject: Re: Datolite locality question  

Mathias wrote:
Dear Kevin thanks for your reply.

Could it perhaps be that the biger crystals, on the first photo, aren't datolite at all, but Calcite? I have some greenish USA (upper new street quarry)- and also Dalnegorsk Datolites in my collection but its difficult for me to compare these with the subject specimen and tell its the same crystallization, lustre, etc. just by the bare eye.

It could easily be tested with some hydrochloric acid, but I try to postpone the destructive analysis a little bit.

Thanks,
Mathias


Mathias,

I have to say, I did wonder (especially as I have collected calcite for many years!), but assumed you would have done a quick hardness test on an inconspicuous crystal face to check, or had other reasons for believing the primary diagnosis.

If you have a piece of fluorite (as I'm sure you do), then if it is datolite it will not be scratched by the fluorite, if it is calcite it will...apologies if this is preaching to the choir!

Kevin

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Mathias




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PostPosted: Jul 31, 2022 13:22    Post subject: Re: Datolite locality question  

Hi Kevin,
I didn't do any testing because the vendor said it is Datolite, but from where he didn't know, which I believed. Now, during our discusion, there"s doubt.
I'll do the tests,
Thanks,
Mathias.
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PostPosted: Jul 31, 2022 13:26    Post subject: Re: Datolite locality question  

The little green crystals in your second photo look more right for datolite
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Mathias




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PostPosted: Aug 05, 2022 14:50    Post subject: Re: Datolite locality question  

Hi, I did an analysis, it is Calcite indeed. Nice pink color in UV light.
That's totally OK with me, I could have done this "research" before asking FMF, but I guess the specimen resembles Datolite sufficiently that I didn't initially doubt the mineral type. I also needed to buy a UV lamp, which I didn't have before.
The specimen could be from many locations, I'll leave that open.
Thanks for all your help because it led to the right determination.
Thanks again.
Mathias.
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