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Sante Celiberti
Joined: 04 Oct 2019
Posts: 699
Location: Tuscany
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 Posted: Nov 03, 2020 16:54 Post subject: Cylindrical calcite crystal? |
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Hello.
We are used to seeing a multitude of calcite habits.
When we come across a cylindrical shape, it is usually stalactitic or coralloid calcite.
How can we interpret this cylindrical crystal, in basaltic rock, with a perfect flat and shiny termination?
Thanks in advance.
Sante
| Mineral: | Calcite |
| Locality: | | Niu Corbu Quarry, Noragugume, Nuoro Province, Sardinia/Sardegna, Italy |  |
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| Dimensions: | 68 x 68 mm |
| Description: |
| The crystal measures 15 mm. |
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8379 Time(s) |
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| Mineral: | Calcite |
| Locality: | | Niu Corbu Quarry, Noragugume, Nuoro Province, Sardinia/Sardegna, Italy | |
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| Dimensions: | 68 x 68 mm |
| Description: |
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| Viewed: |
8360 Time(s) |
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| Mineral: | Calcite |
| Locality: | | Niu Corbu Quarry, Noragugume, Nuoro Province, Sardinia/Sardegna, Italy | |
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| Dimensions: | 68 x 68 mm |
| Description: |
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| Viewed: |
8364 Time(s) |
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Bob Harman
Joined: 06 Nov 2015
Posts: 765
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| Posted: Nov 03, 2020 19:24 Post subject: Re: Cylindrical calcite crystal? |
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Why not Aragonite ?
Yours looks to be a small (1.5 cm) broken aragonite, the other portion of which probably contacted the other side of the small cavity.
See my Indiana example for reference. Bob
| Mineral: | Aragonite on quartz |
| Dimensions: | aragonite is 4 cm in a 9.5 cm geode |
| Description: |
| Self-collected about 15 years ago. |
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8313 Time(s) |
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Josele
Joined: 10 Apr 2012
Posts: 410
Location: Tarifa, Spain
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| Posted: Nov 04, 2020 06:36 Post subject: Re: Cylindrical calcite crystal? |
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Termination seems to be rhombohedral, maybe {021} or {401}. Not well seen in pictures but looks like it has at least another small rhombohedral face at termination.
Could not be an aggregate of small crystals in parallel growth sharing termination faces?
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Sante Celiberti
Joined: 04 Oct 2019
Posts: 699
Location: Tuscany
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| Posted: Nov 04, 2020 08:39 Post subject: Re: Cylindrical calcite crystal? |
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| Bob Harman wrote: | Why not Aragonite ?
Yours looks to be a small (1.5 cm) broken aragonite, the other portion of which probably contacted the other side of the small cavity.
See my Indiana example for reference. Bob |
Hello, Bob. How are you?
Thank you for your kind suggestion.
Your (as usual) beautiful specimen is very indicative.
In fact the quarry also provides many aragonites in needle shape. Unfortunately, the doubt between calcite and metastable aragonite cannot be resolved without sacrificing the crystal. In any case, while for the pseudo-cylindrical shape we could hypotesize - as the friend Josele suggests- a compact bundle of parallel crystals, I cannot explain the perfect (unbroken) and lustrous termination.
Receive warm greetings from Tuscany. Stay healthy.
Sante
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Sante Celiberti
Joined: 04 Oct 2019
Posts: 699
Location: Tuscany
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| Posted: Nov 04, 2020 09:36 Post subject: Re: Cylindrical calcite crystal? |
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| Josele wrote: | Termination seems to be rhombohedral, maybe {021} or {401}. Not well seen in pictures but looks like it has at least another small rhombohedral face at termination.
Could not be an aggregate of small crystals in parallel growth sharing termination faces? |
Hello, Josele. I hope wou are well.
Thank you for your response.
You're right: at the termination there are two small rombohedral facets.
I agree with the parallel growing, but is it possible that these many needles share their termination in such an uninterrupted way to create a unique flat and shining face?This phenomenon occurs in many prismatic crystals (see the beryl, for example), but usually with a small number of crystals. In our case, to justify the pseudo-cylindrical shape, we must imagine a very high number of needles, which makes even more difficult to explain such a strongly shared termination.
Would you consider this a single crystal?
Cordiali saluti.
Sante
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shravigunjal
Joined: 26 Nov 2020
Posts: 1
Location: pune
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| Posted: Nov 26, 2020 23:39 Post subject: Re: Cylindrical calcite crystal? |
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| Great Post
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