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Identity HelpZircon or Spinel?
5th Apr 2018 19:36 UTCNick Gilly
I bought the following specimen on eBay at the weekend, sold as a zircon, and it arrived today. It looks pinker in person than on the photos, particularly in daylight, and some parts with a slight orangey tint show up more orangey under incandescent light. The seller says it's from Nkasi District, Rukwa Region in Tanzania. Here's some pics from the auction:
[img]https://i.ebayimg.com/images/g/40kAAOSwjXVau6Z~/s-l1600.jpg[/img]
[img]https://i.ebayimg.com/images/g/DAUAAOSwtJFau6aE/s-l1600.jpg[/img]
[img]https://i.ebayimg.com/images/g/DDQAAOSwgKBau6aJ/s-l1600.jpg[/img]
[img]https://i.ebayimg.com/images/g/EykAAOSwQqdau6aO/s-l1600.jpg[/img]
[img]https://i.ebayimg.com/images/g/OlwAAOSw629au6Z6/s-l1600.jpg[/img]
[img]https://i.ebayimg.com/images/g/J~YAAOSwQ19au6aT/s-l1600.jpg[/img]
It does have a few gemmy portions, and a nice glassy lustre. I'm not sure if the irregular form is due to parallel growth or etching.
To me it looks like a pinkish-red spinel, probably from Mahenge if it is from Tanzania. The weight is 58 grams. A pity I haven't got a UV light source. It looks like it should fluoresce, although the seller says it doesn't, which is possible if there is appreciable iron in there.
So, am I right? Is this a spinel? It's a lovely specimen whatever it is!
Thanks and regards,
Nick
5th Apr 2018 21:00 UTCScott Rider
And, I'm sure some others would like you to do some testing, hardness for sure, specific gravity, etc. so they can give you a much better opinion. My eye-ball ID says its spinel, but again, not too scientific of an observation...
5th Apr 2018 21:46 UTCNick Gilly
It does scratch quartz, relatively easily too, so I'd estimate a hardness of 8. This would fit with the spinel ID. With zircon I have to press quite a lot harder to make a mark.
I'll have a look at it under the bug killer light at work. Any fluoresence should be fairly obvious I would have thought.
5th Apr 2018 22:03 UTCNick Gilly
http://www.free-form.ch/tanzania/stones/011.jpg
It's also from Mahenge.
5th Apr 2018 22:32 UTCIan Nicastro
6th Apr 2018 17:39 UTCNick Gilly
John Montgomery Wrote:
-------------------------------------------------------
> This is my spinel from Tanzania..
>
John, that is a superb specimen! It also seems to have some other mineral adhering to it like mine, although mine is more orange/rust-coloured, which probably indicates iron oxides. This is apart from the phlogopite mica. One part of the specimen has a small inclusion of a unknown black mineral. Does yours fluoresce?
Actually, I was wondering if Owen Lewis would post his thoughts on this thread too, but I haven't seen any posts from him for a couple of weeks. I hope he's OK.
7th Apr 2018 03:43 UTCDoug Daniels
7th Apr 2018 16:38 UTCNick Gilly
[img]https://farm1.staticflickr.com/866/41297494341_196879abfd_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/870/41297494951_3f149f73fe_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/805/41297495071_71d7c8db1f_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/791/41297495761_27e4228419_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/867/41297496181_9a004eec7f_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/888/41297496501_8b04af34b1_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/805/41297496941_84b120a82c_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/871/41297497721_d107d36bf0_o_d.jpg[/img] - shows black inclusion
[img]https://farm1.staticflickr.com/818/41297498391_238b9fe8c1_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/892/41254710802_1f9554d6ce_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/902/41254711732_c39a6165db_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/883/41297499801_4d196f6a89_o_d.jpg[/img]
[img]https://farm1.staticflickr.com/816/41254712642_6fab096abb_o_d.jpg[/img]
8th Apr 2018 13:56 UTCNick Gilly
I found another spinel that sold recently on eBay that is listed as being from Tanzania:
[img]https://i.ebayimg.com/images/g/dWIAAOSwTmJaoZ2p/s-l1600.jpg[/img]
That has exactly the same association as my specimen: phlogopite mica, and patches of a rusty-looking substance clinging to parts of it. So assuming the country of origin is correct, almost certainly from Mahenge.
12th Apr 2018 17:58 UTCNick Gilly
I'll have to get a new lamp, preferably one that does LW and SW UV.
13th Apr 2018 01:40 UTCAlfredo Petrov Manager
13th Apr 2018 09:07 UTCNick Gilly
I have some money left from a long service award at work and I think I'll buy a UV lamp with it.
13th Apr 2018 17:29 UTCDonald B Peck Expert
Don
13th Apr 2018 22:00 UTCOwen Lewis
Sorry to have been quiet for a while. Been struggling a bit but the last couple of days have been easier and interest in matters more remote than my own anatomy is returning.
If you and Hannah would like to bring your zircon/spinel over on Sunday afternoon we can run a few tests and chat better informed with the results in hand. Thoughts for the moment are as follows:
- Especially from your own photos, I'd guess that your purchase is spinel rather than zircon.
- I have a 365/256 nm UV lightbox we can take a look at it in. It's always interesting but IMHO, UV fluorescence is generally supportive evidence of ID but is frequently short of diagnostic in the cases of zircon, spinel and many other gem crystal. We can play around with some other stuff here under UV too, if you are interested.
- SG. For obvious reasons, an SG test of your complete specimen is not likely to produce a trustworthy result.However, if you are up for it, breaking off a couple of small pieces of the pink crystal should give samples from which reliable results can be obtained. Samples in the range 0.5 - 0.1 ct wt will actually be more reliable (given the lack of crystal transparency) than anything larger is likely to be (given a first-class scale and density determination kit.. Two samples is enough, if the results agree closely. A third sample and averaging the results of all three determinations being necessary if there is appreciable 'spread' in the first two results.
- Hardness. I use the excellent MineralLabs Mohs 2 - 9 styli which (with just a little luck) should sort out zircon from spinel unambiguously..
- Absorption spectra. Worth a peek. The spectra of both a zircon and a pink spinell are usually quite striking and definitive.
- From the translucency of the crystal its likely that testing for anisotropy/isotropy is likely to fail - but always worth a shot.
Mail me if a p.m. Sunday meet is good for you; if not good, suggest something that will work better for you.
13th Apr 2018 22:44 UTCNick Gilly
I'm 99.99% certain that it is a spinel but it would be good to get a confirmation.
15th Apr 2018 13:40 UTCAlfredo Petrov Manager
15th Apr 2018 17:08 UTCDonald B Peck Expert
Don
15th Apr 2018 18:18 UTCFred E. Davis
Transmission of soda-lime glass (common glass) [blue line]:
Transmission of borosilicate glass (Pyrex glass):
From this information, it would appear that copper sulfate transmits UV pretty well. Borosilicate glass passes LW UV better than soda-lime glass, but both block SW UV.
15th Apr 2018 18:54 UTCDoug Schonewald
15th Apr 2018 22:06 UTCOwen Lewis
YMMV but soda glass and some plastics are the common materials for making eye-protecting UV filters. I guess not too many gathered at this watering hole bother to use eye-protection from UV?
16th Apr 2018 01:02 UTCAlfredo Petrov Manager
16th Apr 2018 15:08 UTCFred E. Davis
I believe the plot is for a copper sulfate solution (but I don't have hard evidence). Water appears to transmit UV pretty well, with attenuation the greatest at the orange & red end of the spectrum (making things look green under water).
Fred
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Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 19, 2024 22:50:25