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Identity HelpNeedle Inclusions in tanzanite
8th May 2012 21:20 UTCDawid Godziewski
http://pirop.pl/tanzan/obrazek1.jpg
http://pirop.pl/tanzan/obrazek2.jpg
http://pirop.pl/tanzan/obrazek3.jpg
8th May 2012 22:24 UTCRob Woodside 🌟 Manager
9th May 2012 04:36 UTCRobert Simonoff
However, Jessica and Mike's project could not confirm graphite needles as none were found in that work. They did confirm molybdenite wires/needles.
Bob
9th May 2012 13:22 UTCAnonymous User
But what a nice crystal!
9th May 2012 19:45 UTCJohn A. Jaszczak Expert
9th May 2012 20:10 UTCRonald John Gyllenhammer Expert
I don't have access to this paper but was able to view the abstract. http://gia.metapress.com/content/p96415807v2kk014/fulltext.pdf
Notes on fluid inclusions of vanadiferous zoisite (tanzanite) and green grossular in Merelani area, Northern Thnzania. E. Malisa, K. Kinnunen, and T. Koljonen, Bulletin of the Geological Society of Finland, Vol. 58, No. 2, 1986, pp. 53-58.
Here's an excerpt from the abstract, page 57, left side, halfway down the page.
"... Solid inclusions noted in tanzanite include calcite, gypsum, graphite, rutile, sphene, xenotime,
quartz, diopside, and tremolite-actinolite. Some of these minerals occur as acicular needles which
could impart a cat's-eye effect to some tanzanites."
Ron
9th May 2012 21:32 UTCReiner Mielke Expert
9th May 2012 22:03 UTCRobert Simonoff
Thanks
Bob
9th May 2012 22:50 UTCDawid Godziewski
9th May 2012 23:14 UTCAlfredo Petrov Manager
9th May 2012 23:19 UTCRob Woodside 🌟 Manager
9th May 2012 23:26 UTCRob Woodside 🌟 Manager
9th May 2012 23:33 UTCRobert Simonoff
Bob
10th May 2012 14:31 UTCDawid Godziewski
http://pirop.pl/tanzan/obrazek4.jpg
http://pirop.pl/tanzan/obrazek5.jpg
10th May 2012 16:18 UTCRob Woodside 🌟 Manager
10th May 2012 17:06 UTCRonald John Gyllenhammer Expert
> "...I notice at the bottom of the specimen (where the needles grow), the surface is soft mineral, silver - just like molybdenite !"
Molybdenite and Graphite can appear to be very similiar and so can be a problem to distinguish between the two. If I may suggest, perhaps you can test this area at the bottom of the specimen you mention above as the "soft, silver mineral". Crystalline Molydenite and Graphite have different conductivity properties as I understand it, (when I have more time I'll check the literature on this). If you have a multimeter, perhaps you can check for both continuity and resistance with your leads in this soft silver area at the bottom of the specimen. Graphite should be quite conductive and be positive for a continuity check, with low resistance. Unless heated to high temperatures I don't think you will see these same properties with crystalline Molybdenite, of this I am unsure but again I will check the literature when I have more time.
Further, I suspect that it may be graphite at the bottom of the specimen. Note the above referenced paper for this description "Crystals of tanzanite occur mainly in boudinaged pegmatitic veins and hydrothermal fracture fillings in a brecciated and hydrothermally altered graphite-bearing diopside gneiss. Associated minerals include quartz, diopside, graphite, calcite, hematite, and sphene, as well as green vanadian grossular garnet."
Now whether or not these acicular inclusions are indeed Graphite remains to be proven for this specimen but intuitively it would seem that there could be a correlation between the acicular needles and the "soft silver mineral at the base". All this speculation is just that, especially since this is just a silly "remote viewing" effort from only images. I have not personally seen Graphite as a acicular inclusion like this but then again, there's alot I haven't seen. Also, I am always hesistant to disagree with Rob since he is very often correct. :-) Someone like John Jaszczak who has studied Graphite in depth may have a better perspective than me on the possibility of Graphite as an acicular inclusion here. BTW Dawid, It's a truly beautiful and wondrous specimen. Good luck with it and all the best.
Ron
10th May 2012 17:51 UTCRob Woodside 🌟 Manager
10th May 2012 18:23 UTCRobert Simonoff
The silver, on the bottom, could be graphite, just not associated with the acicular mineral, but instead coincident. I agree with the testing, especially, since this does look like mauled graphite that is so common on the matrix of these pieces.
I see 2 other minerals at the bottom of this piece, one is tan and could be titanite or zoisite - as per the Mineral News paper. The greenish mineral could be garnet or diopside - again the Mineral News paper found both to be in similar green colors in association here. The colors appeared similar especially when the crystals were small, such as that one is.
Bob
10th May 2012 20:10 UTCRonald John Gyllenhammer Expert
I was unaware of this paper on which Jessica is a listed author, Simonoff J., Wise M (2012) A closer Look at Merelani Minerals., Mineral News Vol 28 No 2. I do not have this issue but will make an effort to get it and look forward to reading it. Concerning the Molybdenite wire, was this found as an inclusion or otherwise? All the best.
Ron
11th May 2012 03:32 UTCRobert Simonoff
Bob
12th May 2012 18:51 UTCRob Woodside 🌟 Manager
Does anyone know the cause of the blue colour in Tanzanite?
Could it be trace Molybdenum? Does the heating change the oxidation state of Mo to give the blue colour? Molybdenite and Ilsemannites are blue and the blue appears more intense around the needles in this tanzanite. This is rank speculation; but if true, then Mo should show up in an ICP analysis.
13th May 2012 03:29 UTCRobert Simonoff
Rob, the color of tanzanite, according to Bernard Olivier's thesis on Merelani, is largely Vanadium (V3+ substituting for Al3+) within the crystal structure (blue violet coloring). the range seems to be between 972 and 6196 ppm in his study. He used spectroscopic and EPR analysis, which also shoed that the Ti4+/Ti3+ ratio within the structure was also important. Heating tanzanite causes an exchange:
Ti3+ V4+ -> Ti4+ V3+ (which increases the amount of blue/violet coloring)
Green zoisite seems to have more Ti than the other colors of zoitite
Blue ziosite seems to have the highest concentration of V
Colorless has the lowest concentration of V
Orange zoisites seems to have Sr substituting for Ca (not entirely tested in the paper) and Nd3+ substituting for Al3+
Note: I do find that the same work did identify tremolite-actinolite needles included in some tanzanite. I am not sure, however if this was tested or assumed (as the graphite needles were assumed).
If anyone wants to read this tome, it can be found here: http://scholar.sun.ac.za/handle/10019.1/1093
Bob
13th May 2012 06:18 UTCRalph S Bottrill 🌟 Manager
13th May 2012 15:57 UTCRob Woodside 🌟 Manager
15th May 2012 03:29 UTCJohn A. Jaszczak Expert
Considering how much graphite there is in the world, molybdenite associated with graphite is probably rare; nevertheless,
I have molybdenite on graphite from Lime Crest quarry, NJ and graphite crystals on a molybdenite crystal from Moshi, Tanzania.
The latter is not far from Merelani. (Both are TINY)
Cheers,
John
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