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Cylindrical calcite crystal?
  
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Sante Celiberti




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PostPosted: Nov 03, 2020 16:54    Post subject: Cylindrical calcite crystal?  

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



IMG_20201103_183238.jpg
 Mineral: Calcite
 Locality:
Niu Corbu Quarry, Noragugume, Nuoro Province, Sardinia, Italy
 Dimensions: 68 x 68 mm
 Description:
The crystal measures 15 mm.
 Viewed:  802 Time(s)

IMG_20201103_183238.jpg



IMG_20201103_184625.jpg
 Mineral: Calcite
 Locality:
Niu Corbu Quarry, Noragugume, Nuoro Province, Sardinia, Italy
 Dimensions: 68 x 68 mm
 Description:
Lateral view.
 Viewed:  794 Time(s)

IMG_20201103_184625.jpg



IMG_20201103_184805.jpg
 Mineral: Calcite
 Locality:
Niu Corbu Quarry, Noragugume, Nuoro Province, Sardinia, Italy
 Dimensions: 68 x 68 mm
 Description:
Closer view.
 Viewed:  793 Time(s)

IMG_20201103_184805.jpg


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Bob Harman




Joined: 06 Nov 2015
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PostPosted: Nov 03, 2020 19:24    Post subject: Re: Cylindrical calcite crystal?  

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



fullsizeoutput_3650.jpeg
 Mineral: Aragonite on quartz
 Dimensions: aragonite is 4 cm in a 9.5 cm geode
 Description:
Self-collected about 15 years ago.
 Viewed:  749 Time(s)

fullsizeoutput_3650.jpeg


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Josele




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PostPosted: Nov 04, 2020 06:36    Post subject: Re: Cylindrical calcite crystal?  

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




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PostPosted: Nov 04, 2020 08:39    Post subject: Re: Cylindrical calcite crystal?  

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




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PostPosted: Nov 04, 2020 09:36    Post subject: Re: Cylindrical calcite crystal?  

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



IMG_20201104_124940.jpg
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 Viewed:  592 Time(s)

IMG_20201104_124940.jpg


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shravigunjal




Joined: 26 Nov 2020
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PostPosted: Nov 26, 2020 23:39    Post subject: Re: Cylindrical calcite crystal?  

Great Post
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