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Jason
Joined: 31 Dec 2008
Posts: 254
Location: atlanta
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 Posted: Mar 18, 2010 17:12 Post subject: Cobalt bearing spinel from Pakistan |
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| Elise wrote: | Meanwhile today I was helping a friend with samples he just brought back from Pakistan a couple months ago(by way of entering through China) - wonderful cobalt spinel, red spinel and ruby all in matrix, along with red zircon in matrix (Skardu District). Fun to examine.
Elise |
hmm..cobalt bearing spinel from pakistan..never seen or heard of a reference of Co from pakistan..are you sure it's pakistani? I have sold quite a few real deal cobalt spinels in my day too..not "cobalt blue" but real coloring chromophore cobalt spinels..never heard of any from pakistan or afganistan
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Jordi Fabre
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Joined: 07 Aug 2006
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Location: Barcelona
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| Posted: Mar 20, 2010 15:10 Post subject: Re: Cobalt bearing spinel from Pakistan |
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| Elise wrote: |
Hi - I am sorry I didn't see your question earlier and reply. My friend is a bit of an adventurer, prospector and mineral collector - always has intriguing specimens for me to look at. Actually, he did not refer to it as cobalt spinel, I did. Sometimes there isn’t any way to determine the cobalt content without advanced lab work, which the specimens haven’t had yet, so you are correct that I probably should not have called it so -- though the lovely blue crystals bedded in white marble were quite wonderful in contrast and arrangement, despite whatever causes their color. To be honest I was more interested in the “locally grown” calcite and was only having a quick look at the spinels with a handheld diffraction spectroscope and a Chelsea filter (= red).
Never-the-less, it is good to remember that sometimes the Co causing the color is so low in concentration that EDXRF won’t detect it, though UV-vis indicates its presence. I haven’t looked at it with a desktop spectroscope yet, but even so, that may not show even weak Co bands. It takes relatively minute concentrations to cause a blue color as intense as that caused by higher concentrations of iron. It can be anywhere from non-detectable to 0.05 % by wt; in fact, a spinel has been reported colored blue by cobalt with as little as 0.00053% - that is 5.3 ppm.
As for locality – Hunza Valley, Pakistan. A quick note to a colleague in Bangkok confirmed it as a known locality for cobalt spinel, and indeed if you check back through the literature, you will see that Dr. Gübelin reported this as early as 1982.
Best wishes,
Elise
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Elise Skalwold
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Jason
Joined: 31 Dec 2008
Posts: 254
Location: atlanta
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| Posted: Mar 21, 2010 12:42 Post subject: Re: Cobalt bearing spinel from Pakistan |
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| If Co is causing the color regardless of amount present it will show up on spectrograph. Thats pretty cool..about 90% of all the stones I sell are pakistani and afghan in origin and I have never seen or been offered any Co spinel or even blue spinel from pakistan nor have I ever sold a Co spinel gem with it's origin from pakistan.....really had no idea..Richard Hughes and Vincent Pardiaeu never mentioned it either...learn something new every day..do you have any reference material you can link me to with any info about them, location, or just blue/Co bearing spinel from pakistan in general? Thanks Elise
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Elise
Joined: 22 Dec 2009
Posts: 243
Location: New York State
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| Posted: Mar 24, 2010 13:09 Post subject: Re: Cobalt bearing spinel from Pakistan |
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| amethystguy wrote: | | ..about 90% of all the stones I sell are pakistani and afghan in origin and I have never seen or been offered any Co spinel or even blue spinel from pakistan nor have I ever sold a Co spinel gem with it's origin from pakistan.....really had no idea.. |
From what you are saying, you sell cut stones or faceting rough; I would suggest that you have your material tested if you are selling them as such. Probably the easiest articles for you to access would be in Gems & Gemology-- regarding this locality: "Gemstones of Pakistan, Emerald, Ruby and Spinel by Dr. Gübelin (F82) and probably the first definitive paper on the subject: "Cobalt-Blue Gem Spinels" by Dr. Shigley and C. Stockton (Sp84). There are several others since and in other publications. My thought that these are cobalt spinels is based on a weak Co spectrum and a bright red Chelsea filter reaction. As I said previously, my information about cobalt-bearing spinels being from that locality is anecdotal, though from someone who knows the area and knew Dr. Gübelin.
Meanwhile, back to mineral specimens: last night we were treated to a travelogue of adventure through the mountains and valleys of China and Pakistan's Hunza Valley which brought to life the descriptions of Dr. Gübelin and others who have explored these areas. It was fascinating to once again examine a few of the specimens, this time in the company of a mineralogist, and to put them in context of the locality while looking at maps and pictures. I don't have measurements of the crystals below, but the ruby crystal is about 30mm long and not nearly as purple as my picture implies; it is in fact very very red! The spinels and rubies burned bright in the UV box under LW - great fun. I made a "still-life" to share here, with a close-up of the blue spinels and a crystal suite which has feldspar, scapolite and a yet unknown dark crystal. This little arrangement of specimens reminds me that spring is coming and along with it, flowers.
Best wishes,
Elise
PS - Jordi - since it is now out of context, may I just note for the readers that this thread was split from my calcite posting : https://www.mineral-forum.com/message-board/viewtopic.php?p=10749&highlight=#10749
| Description: |
| Garden of Crystals from Hunza Valley Pakistan: Ruby Corundum, Purple Corundum, Red Spinel, Blue Spinel, Green Pargasite; all in white marble matrix with phlogopite here and there. |
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20749 Time(s) |
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| Description: |
| Spinel, Hunza Valley Pakistan |
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20706 Time(s) |
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| Description: |
| Feldspar, Scapolite and unknown dark crystal, Pakistan |
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20687 Time(s) |
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Elise Skalwold |
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Jason
Joined: 31 Dec 2008
Posts: 254
Location: atlanta
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| Posted: Apr 04, 2010 12:51 Post subject: Re: Cobalt bearing spinel from Pakistan |
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missed your reply elise..great pics..i get all my cobalts spectra..makes a big difference when selling..stand out in the flood of unsavory sellers with "cobalt blue" spinels..lack of gray mask is the best thing about cobalt as opposed to an iron colored blue...I am going to copy your post and post someplace else if thats okay with you..other place doesn't allow outside links so i have to copy and paste ..so you saw Co lines..what range by chance? don't and won't ever trust the chelsea filter..not good foir anything but cleaning toilets..not even good for emeralds anymore..thanks
jason
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Elise
Joined: 22 Dec 2009
Posts: 243
Location: New York State
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| Posted: Apr 07, 2010 20:22 Post subject: Re: Cobalt bearing spinel from Pakistan |
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| amethystguy wrote: | | ........ don't and won't ever trust the chelsea filter..not good foir anything........ |
I hope this doesn't mean you threw out the baby with the bathwater as well. I have a drawer full of filters of all sorts, a spectroscope with several different color-filter settings and the built-in filters (yellowing corneas) inherent to those of us in the over-50 crowd who are just trying to make out those absorption lines down in the near 400 nm blue range. Minerals act as filters themselves when light passes through - I encourage you to play with the CF and see what you what you can discover; you might find it is useful in combination with other criteria.... or just pure fun.
Just a thought from someone who owns many styles of shades (filters)... amber (for driving), polaroid (for sailing), rose (for Mondays),
Elise
"Well, when I cleaned up my diction, I had nothing left to say."
(Van Morrison).
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Elise Skalwold |
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Jason
Joined: 31 Dec 2008
Posts: 254
Location: atlanta
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| Posted: Apr 07, 2010 22:45 Post subject: Re: Cobalt bearing spinel from Pakistan |
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| Dr. Hanneman has many cool things that can be used with the CH filter..most top gemmo's i know won't even touch one..it's a trade off..using one for Co spin. is good and works but as you know it was made for emeralds..so checking for chromium in other things can give you weird readings..keep the good post coming
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