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Re: Cordierite

Posted by Olav Revheim  
Re: Cordierite
July 10, 2010 03:06PM
Rock that is an excellent article. The only minor quibble I would have is with the brief section on the possible use of cordierite as a navigation aid. For a number of reasons, many researchers think it is much more likely that iceland spar (calcite) was used as a navigation aid.

There was a brief discussion about it on this message board, here:

Iceland spar discussion
avatar Re: Cordierite
July 11, 2010 02:14AM
Kelly, Thanks for your note. I will immediately severely chastise the author for that laps. Well not really, and I am sure that in good time, Olav will come along and address your comment about Iceland spar which sounds reasonable to me. Perhaps they were both used.

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
July 12, 2010 10:56AM
it    
Hi Rock, I would like to point also the interesting occurrence of cordierite crystals in southern Tuscany, Italy, spreaded into the magmatic materials of Roccastrada – Roccatederighi, Grosseto Province. This cordierite has a magmatic origin, and it has a particular importance and meaning because its occurrence in these acid lavas is probably related with anatectic origin.

In Roccastrada-Roccatederighi area there are occurrences of rhyolitic lava domes and also of small exogenous estrusions of these magmas. One of the most “famous” rhyolite domes occours just near (and under) of the village of Roccatederighi. The rock is usually deeply altered, but there is still possible to recognize and find quartz, the sanidine (K-feldspar up to 10 cm!), biotite and less plagioclase. As accessory minerals in these lavas there are cordierite crystals, occurring as euhedral-subhedral up to anhedral crystals, generally not greater than 15-20 mm and mostly altered more or less deeply, into pinite which gives to them a greenish, brownish coating. However I have seen specimens with small xls (not more than 4 mm) still “fresh” showing a pale violet colour.

These rhyolitic rocks are very interesting just for the presence of cordierite, which it is index of a peraluminous character really similar with most of monzogranites and the other rhyolites (of our so called "Tuscan Magmatic Province”) all highly Al rich and suggesting an anatectic origin , for fusion of probably meta-sedimentary previous rocks.

[www.mindat.org]

[www.mindat.org]



Edited 3 time(s). Last edit at 07/12/2010 11:11AM by Marco Barsanti.
avatar Re: Cordierite
July 12, 2010 08:56PM
Marco,
That quite interesting and it should rate an entry in the Cordierite article. I suspect that Oliv will be along shortly and make the entry. If not eventually someone else will take up the article and revise it. You put the information in exactly the right place so that it can't be ignored or forgotten like a lot of stuff that gets entered in some of the other message forums. When I catch something interesting in the other forums I try and copy it to the appropriate mineral here in Best Minerals so it worn't get lost.

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
July 13, 2010 07:48AM
it    
Great work, Rock,

ewhen i have time, ill check oher minreals and i'll mesasage you if i have added something, just as a reminder...

Ciao!
avatar Re: Cordierite
July 13, 2010 08:37PM
Marco,
Thanks very much. The reason we put Best Minerals in the Message board was so that anyone who wanted to could contribute here under the mineral and the locality that they new about. Here is a place to put all that stuff that we learn as collectors about specimens and their localities.

Rock Currier
Crystals not pistols.
Re: Cordierite
September 02, 2010 06:30PM
no    
I am "back in business" on this article, and I would like to thank everyone for their valuable contributions so far. There is a lot of great information and new cordierite pictures yet to be included in the article. I have not yet been able to embed all, but I've restarted from the top and will eventually get there. Comments and feedback are welcome.
Olav

Olav, Ive gone into the article and tweaked the images and did a few other clean up chores to try and help out.
Rock




Edited 1 time(s). Last edit at 09/03/2010 01:36AM by Rock Currier.
Re: Cordierite
September 25, 2010 08:36PM
no    
I've come as far as I get on this article now. There are still some information missing, and there are useful photos attached to messages and not upkoaded to the database. I would really like to use them in the article.
These are
the ones from the Stall Lake Copper Mine posted by Bob Southern
the ones from the Ivory Coast, posted by Stephane Mouthon
the ones from Richmond on Tom Mortimer's home page. There is a few posted there that would fit neatly in.

I would also like to learn more about size and availability of cordierites from

France
Brazil
Madacascar
India
Tanzania

Thanks a lot for all contributions.

Olav
avatar Re: Cordierite
September 25, 2010 09:45PM
Olav,
You have done a really excellent job on the Cordierite article. I went in and did a bit of tweaking to make for formatting look a bit better. I thought you did an excellent job on the text that accompanies many of the entries. I thought the bit about how local Japanese collectors treat their specimens was particularly interesting. If you have not already tried, you might contact the three individuals that you mention and see if they will upload their images to mindat, or in the worst case ask them to send you the images so you can upload them to mindat. I do this in some cases in a pinch but you have to find out if they took the photo and if not, who holds the copyright. It is a bit of a bother that I usually don't bother with because there is so much stuff to do on this project that I think it better to move on in most cases and trust that with time that they or others will upload similar or better images.

Luiz Menezes says he will shortly be in a position to help out with Brazilian information, and if you sent him a private message perhaps he could help you out with more information about Brazilian Corderite localities.

Have you decided yet on another mineral you would like to do a best minerals article about? Its a lot of work, isn't it? But remember, no more than 60 hours a week!

Rock Currier
Crystals not pistols.
Re: Cordierite
April 12, 2013 07:54AM
A discrete find of partly unaltered, sharp euhedral, aquamarine blue colored cordierite crystals up to 10 cm was made during the fall 2012 in the Bamble sector, Norway. Multiple images are available from: [www.mindat.org].
Kind regards,
J Kihle
avatar Re: Cordierite
April 12, 2013 11:03AM
Jan, Thanks for pointing them out. Yes, some of them will probably be added to the article along with some of your comments about them.

Rock Currier
Crystals not pistols.
Re: Cordierite
April 12, 2013 12:36PM
no    
Jan

I am sorry that I did not update the article with your input when I got your e-mail, but I have finally included some of your photos in the article. I am very grateful that you chose this best minerals article as one the channels for publishing this great find.

Olav
Re: Cordierite
August 01, 2013 09:01PM
Hi Rock:

I had a specimen I brought a a show a number of years ago that was labeled cordierite. Its blue and comes according to the label, from MALACACHETA, MUCURI VALLEY, MINAS GERAIS, BRAZIL NO CRYSTALS But a gemmy crystal structure in shist like rock with pyrope garnet. Though let you now.
avatar Re: Cordierite
August 02, 2013 10:02PM
Richard,
Thanks for that bit of information. Ill leave it for our Brazilian expert Luiz Alberto Dias Menezes to make use of it if he considers it to be a valid locality.

Rock Currier
Crystals not pistols.
Re: Cordierite
August 03, 2013 04:14AM
Hi Olav,

I miss a really well-known locality for big (up to 15 cm) "pinite"-pseudomorphs of cordierite in Austria (Lisens valley, Tyrol, also well-known for its good andalusite crystals). Unfortunately, I have currently no possibility to look for my own (self-collected) specimens in my collection, because I am in China for business. Maybe, someone can provide more information about and especially pictures of these well-formed pseudomorphs.

Volkmar
Re: Cordierite
August 03, 2013 06:46AM
no    
Volkmar,

Thank yousmiling smiley. I will add the Lisens Alps to the cordierite article as I have done for the andalusite article.

Photos and information on this and localities will be appreciated

thanks

Olav
Re: Cordierite
August 03, 2013 06:47AM
no    
Richard,

Thank you for your information, I will investigate this locality further.

Thanks
Olav
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