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Jordi Fabre
Overall coordinator of the Forum
Joined: 07 Aug 2006
Posts: 5028
Location: Barcelona
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 Posted: Jul 31, 2017 09:37 Post subject: Calcite seen at Sainte-Marie-aux-Mines Show 2017 |
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| In Sainte Marie-aux-Mines Show 2017 Roger Warin wrote: |
Hi,
After the visit of the Show of Ste-Marie 2017, I propose some photos.
In the first place, a historical calcite of Des Cloizeaux highlighting a new form for the time.
I suggest to Pete Richards to explain this crystal to us by a drawing.
Roger.
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| Mineral: | Calcite |
| Locality: | | Røde Fjord, Sermersooq, Eastern Region (Austurland), Iceland |  |
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| Dimensions: | 10 - 12 cm |
| Description: |
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| Viewed: |
7515 Time(s) |
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| Mineral: | Calcite |
| Locality: | | Røde Fjord, Sermersooq, Eastern Region (Austurland), Iceland | |
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| Dimensions: | Detail |
| Description: |
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| Viewed: |
7506 Time(s) |
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Pete Richards
Site Admin
Joined: 29 Dec 2008
Posts: 843
Location: Northeast Ohio
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| Posted: Jul 31, 2017 12:23 Post subject: Re: Calcite seen at Sainte-Marie-aux-Mines Show 2017 |
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| Jordi Fabre wrote: | | In Sainte Marie-aux-Mines Show 2017 Roger Warin wrote: |
Hi,
After the visit of the Show of Ste-Marie 2017, I propose some photos.
In the first place, a historical calcite of Des Cloizeaux highlighting a new form for the time.
I suggest to Pete Richards to explain this crystal to us by a drawing.
Roger.
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Hi Roger and all,
I cannot totally explain this calcite crystal from Iceland, but I can provide some information. As Roger said, this is a significant historical specimen from an important early crystallographer which is the "type specimen" for a new crystal form for calcite. For a crystallographer, this is analogous to finding a new species for a mineralogist.
The label contains five lines of information, the first of which appears to be a catalog number or similar identification. The second give the form a name, N, and a set of numbers that are analogous to Miller indices, but using a different notation which I have forgotten how to translate into Miller indices, if I ever knew how. The third line indicates that this is a new form. The fourth line provides the important information that the angle measured between two adjacent faces of the form (the interfacial angle) is 158°25', and the last line indicates that the theoretical (calculated) angle is the very similar 158°31', one tenth of a degree different.
One problem with letter names for crystal forms is that not everyone uses the same letters for the same forms. Goldschmit's Atlas has a table for each mineral showing what letters have been used for what forms, and by whom. Really confusing!
Dana's System of Mineralogy, 6th edition (1892) provides a table of Miller indices for calcite along with the letter names he used for them, The form N {4.16.-20.3} is included. SHAPE allows the form to be drawn (see below), and also can calculate the interfacial angle for N, which, happily, is 158°30.63', the same angle as the computed one from the label, to the nearest minute. This pretty much assures that the N of Dana is the same as the N of Des Cloizeaux.
The faces in the middle front of the crystal image that form a V-shape are most likely members of the form N {4.16.-20.3}. The other faces have letters on them in ink, indicating their indices, but I do not know how to translate them. One of the mirror planes of calcite is apparent running down the middle of the crystal as imaged. The crystal is clearly incomplete.
The SHAPE drawing below shows N {4.16.-20.3} in combination with {0001}. The retouched image from Roger's photograph shows the faces thought to belong to N and the trace of the mirror plane on the surface of the crystal.
| Description: |
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| Viewed: |
7479 Time(s) |
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| Description: |
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| Viewed: |
7560 Time(s) |
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_________________
Collecting and studying crystals with interesting habits, twinning, and epitaxy |
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Pete Richards
Site Admin
Joined: 29 Dec 2008
Posts: 843
Location: Northeast Ohio
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| Posted: Jul 31, 2017 12:47 Post subject: Re: Calcite seen at Sainte-Marie-aux-Mines Show 2017 |
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A bit of further research reveals the variety of systems used to describe the orientations of crystal faces, analogous to Miller indices. Dana's System 6th edition decribes the Naumann index system in some detail, and mentions systems of others: Weiss, Mohs and Haidinger, Hausmann, Lévy, Goldschmidt, "and others"!
It also says "the symbols of Lévy are (1892) extensively used in France", so probably these are the symbols used on the label.
It also says that a detailed comparison of all these systems is provided in Goldschmidt's Atlas of Crystal Forms. I leave it up to the interested reader to pursue this matter in more detail!
_________________
Collecting and studying crystals with interesting habits, twinning, and epitaxy |
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Roger Warin
Joined: 23 Jan 2013
Posts: 1232
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| Posted: Aug 01, 2017 03:09 Post subject: Re: Calcite seen at Sainte-Marie-aux-Mines Show 2017 |
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Hi Pete, all,
Thank you for this beautiful demonstration realized with such acuity.
The enlarged label shows
e7/3
N = (d1/9 d 1/5 b 1/4 )
Nouveaux (new forms)
e7/3 = {10.0.-10.1}
This rhomboedron seems unknown before Des Cloizeaux.
There are still other annotations on the crystal, particularly
d2 inf inférieur ? d2 = {2 1 -3 1}
Also maybe e1/ 3. Very difficult to read.
Roger.
| Mineral: | calcite Des Cloizeaux's label |
| Description: |
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| Viewed: |
7324 Time(s) |
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