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Pseudoctahedral Calcite
  
  Index -> Rockhounding trips
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dontgogreen




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PostPosted: Nov 06, 2016 21:01    Post subject: Pseudoctahedral Calcite  

There is a large roadcut in West Virginia along Corridor H where I have found a variety of minerals such as quartz, calcite, strontianite, and sulfur. They are not particularly flashy or large specimens, in fact a prominent collector described them as "homely", but I did notice that many of the calcites have a psuedoctahedral habit. Can anyone comment on the occurrence of this habit in calcite?


calcite1.jpg
 Mineral: Calcite
 Locality:
Corridor H roadway, West Virginia, USA
 Dimensions: Crystal = 4mm
 Description:
 Viewed:  6703 Time(s)

calcite1.jpg


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dontgogreen




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PostPosted: Nov 06, 2016 21:02    Post subject: Re: Pseudoctahedral Calcite  

A second specimen


calcite2.jpg
 Mineral: Calcite
 Locality:
Corridor H roadway, West Virginia, USA
 Dimensions: Crystal = 4mm
 Description:
 Viewed:  6670 Time(s)

calcite2.jpg


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dontgogreen




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PostPosted: Nov 06, 2016 21:03    Post subject: Re: Pseudoctahedral Calcite  

A third


calcite3.jpg
 Mineral: Calcite
 Locality:
Corridor H roadway, West Virginia, USA
 Dimensions: Crystal = 4mm
 Description:
 Viewed:  6654 Time(s)

calcite3.jpg


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dontgogreen




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PostPosted: Nov 06, 2016 21:10    Post subject: Re: Pseudoctahedral Calcite  

These calcites occur in a vuggy limestone, about one foot in thickness that dips about 45 degrees. The area has undergone quite a bit of deformation in the form of folding. There are several of these calcite-producing layers at this particular outcrop, however the majority of the limestone and shales here are barren of minerals. This particular layer produces the pseudoctahedral calcites in association with powdery strontianite. Some small strontianite sprays were located nearby, but not within this layer where it was usually in massive pods of about 1-3in.


calcite4.jpg
 Mineral: Calcite
 Locality:
Corridor H roadway, West Virginia, USA
 Dimensions: 5.1cm
 Description:
 Viewed:  6674 Time(s)

calcite4.jpg


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Mark Holtkamp




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PostPosted: Nov 07, 2016 07:14    Post subject: Re: Pseudoctahedral Calcite  

Long time ago there was an article in Lapis magazine about a pseudo-octahedral crystal from the Juchem quarry in Germany. I also found one for sale on minfind, from Aussig in the Czech Republic.

These crystals are probably a combination of a suitable rhombohedron (e.g. {301} and the base pinacoid.

https://www.smorf.nl/draw.php?json=q_a1UtI1NtLPVdLxs_LXCbCqdrQy1HECYmcrAz0LUxOdQCtLA50gEBFsZWhkUKsTYhVd7WFloOMNxD5AhS5WhrU6QBFjFJHYWgA=
(link normalized by FMF)

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Pete Richards
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PostPosted: Nov 07, 2016 09:01    Post subject: Re: Pseudoctahedral Calcite  

Pseudo-octahedral calcite has also been found in other places. There was an article in the last 10 years about an Australian example (sorry not to have a better citation). Pseudo-octahedral calcite crystals were found in a boulder at the Minesota Mine in Michigan's Upper Peninsula, and described in Rocks & Minerals by Pete Rodewald and me. See R. Peter Richards & Peter Rodewald (2008) Pseudo-Octahedral Calcite from The Minesota Mine, Ontonagon County, Michigan, Rocks & Minerals, 83:4, 308-313, DOI: 10.3200/RMIN.83.4.308-313.

These crystals turned out to be a complex combination of four forms. The summary figure is appended below.



Calcite.jpg
 Mineral: Calcite
 Locality:
Minesota Mine (Minnesota Mine), Rockland, Ontonagon County, Michigan, USA
 Description:
 Viewed:  6508 Time(s)

Calcite.jpg



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prcantos
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PostPosted: Nov 07, 2016 13:06    Post subject: Re: Pseudoctahedral Calcite  

I can provide a graphical approach where the rhombohedron {301} is changed into a pseudoctahedron by a combination with the pinacoid {001}, according to

Mark Holtkamp wrote:
These crystals are probably a combination of a suitable rhombohedron (e.g. {301} and the base pinacoid.



CalcitePseudoctahedron.jpg
 Description:
 Viewed:  6442 Time(s)

CalcitePseudoctahedron.jpg



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dontgogreen




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PostPosted: Nov 07, 2016 13:16    Post subject: Re: Pseudoctahedral Calcite  

The crystal drawings shown by Mr. Richards are more similar to a true octahedron than the crystals I have found. Each of these pseudo-octahedral crystals has one face that is terminated by a very low-angle rhombohedron, but since the crystals are almost equant in dimension, they appear octahedral from many angles.
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Pete Richards
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PostPosted: Nov 07, 2016 17:50    Post subject: Re: Pseudoctahedral Calcite  

As a purely geometric exercise, there are a number of possible ways to make a calcite crystal that looks somewhat like an octahedron. Some of these are unlikely, if the forms used to make them are rare or unknown on calcite. Palache's table of calcite forms, though dating from the 1940's, is the Bible for calcite forms. He does not list {30-31} as a known form, which is problematic for its proposed use in this discussion. He does list {03-31} which is identical in "steepness" but rotated by 60° relative to {30-31}; it could contribute to an "octahedral" crystal of the same appearance, but it is also an uncommon form.
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dontgogreen




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PostPosted: Nov 29, 2018 11:14    Post subject: Re: Pseudoctahedral Calcite  

We made another trip back to this area to see what had turned up. It took about half an hour to gather a large quantity of grey vuggy limestone riddled with calcite crystals. Many of the large pieces make excellent bookends and decorator pieces. Under the microscope, the crystals exhibit different, more complex forms than those collected previously. Additionally, breaking open some massive vein material revealed native sulfur and fluorite (mostly broken) associated with orange iron staining, probably from the dissolution of sulfides. The occurrence of native sulfur and purple fluorite makes me wonder if perhaps a pyrite crystal was weathered, allowing the sulfur to crystallize in its native state and allowing the iron to color the fluorite. This is just speculation.

I also learned that a large cave had been opened near this area several years ago during road construction. The team that explored it took lots of photos which can be seen here:

https://www.tristategrotto.net/Bob/Scherr%20Crystal%20Cave/album/index.html
(link normalized by FMF)

After exploration, the cave was sealed, and its whereabouts are unknown to the public. From the available info, I gather that it is quite close by to this locality.



collecting.jpg
 Description:
near Scherr, West Virginia
 Viewed:  1300 Time(s)

collecting.jpg



Calcite3.jpg
 Mineral: Calcite
 Description:
near Scherr, West Virginia
FOV 1 cm
 Viewed:  1296 Time(s)

Calcite3.jpg



IMG_20181129_104921764.jpg
 Mineral: Calcite
 Description:
near Scherr, West Virginia
30 cm
 Viewed:  1298 Time(s)

IMG_20181129_104921764.jpg



IMG_20181129_105103770.jpg
 Mineral: Sulfur, fluorite, calcite
 Description:
near Scherr, West Virginia
~15 cm each
 Viewed:  1303 Time(s)

IMG_20181129_105103770.jpg


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makokerowill




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PostPosted: Nov 29, 2018 13:07    Post subject: Re: Pseudoctahedral Calcite  

Buenas tardes amigos !
Conocéis algún yacimiento español donde hayan aparecido calcitas pseudo-octaédricas ?Saludos.
dontgogreen wrote:
There is a large roadcut in West Virginia along Corridor H where I have found a variety of minerals such as quartz, calcite, strontianite, and sulfur. They are not particularly flashy or large specimens, in fact a prominent collector described them as "homely", but I did notice that many of the calcites have a psuedoctahedral habit. Can anyone comment on the occurrence of this habit in calcite?
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Jordi Fabre
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PostPosted: Nov 29, 2018 13:10    Post subject: Re: Pseudoctahedral Calcite  

makokerowill wrote:
Buenas tardes amigos !
Conocéis algún yacimiento español donde hayan aparecido calcitas pseudo-octaédricas ?Saludos.
dontgogreen wrote:
There is a large roadcut in West Virginia along Corridor H where I have found a variety of minerals such as quartz, calcite, strontianite, and sulfur. They are not particularly flashy or large specimens, in fact a prominent collector described them as "homely", but I did notice that many of the calcites have a psuedoctahedral habit. Can anyone comment on the occurrence of this habit in calcite?

This is an English language Forum. Please ask your question in the Spanish side. Thank you.
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