Post subject: Re: Usual and unusual gemstones and inclusions
Posted: Wed Apr 27, 2016 8:26 pm
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Joined: Sun Oct 16, 2005 1:44 pm Posts: 1025
GSK wrote:
Inclusions in Canadian andradite - demantoid (Asbestos, Jeffry Mine). Chromite crystal (as referenced by local specialists) and byssolite fibers (horsetail). Together with some other samples has been purchased at Montreal Mineral show just day before...
Pictures are a bit blurry because through natural unpolished facets...
Not much as I know.. Оr more correct to say - I don't know too much about... Having soon ~ 300 crystals will be good chance for research...
Talking with guys from Ural, professionally working (mining and faceting) demantoids from there, I found their opinion - Canadian crystals when not alluvial and not destroyed show different form of crystal. Also most of Canadian's have chromite crystals instead of magnetite mostly found in Ural's(not sure if it is correct about Ural's), but Persian as I know also have mostly chromite. Anyway these crystal's inclusion can not pretend to be origin determination factor.
The main thing maybe - identification of fiber's mineral nature itself. Ural's are byssolite or canals left after its dissolving (again - if I am not wrong), in Canadian I suspect possibility some kind of asbestos. Especially looking at this "hairy" crustal.. But it has to be tested.
All I said - not any kind of scientific fact. Just discussions and guesses.
_________________ All stones are alike, all stones are precious; but man sees only a few of them... Maurice Maeterlinck
Byssolite is asbestos, though specifically amphibole asbestos (and usually actinolite-tremolite). Outside of particularly expensive equipment and rather invasive testing, how would you distinguish chromite and magnetite? They're both opaque, black spinel-group minerals, and there's complete solid solution between the two.
Stephen, myself - I am not able to distinguish chromite and magnetite. Crystals are going to be sent to a few research centers in Europe where all advanced equipment is available and being used. I rather have same equipment too at my home-lab, but presume - next life only...
"Byssolite" and "asbestos" - I guess I said it incorrectly, byssolite, chrysotile together with a few other are different types of asbestos as I understand. I meant - different types could be found in crystals from that and this location. Again it is only guessing.
_________________ All stones are alike, all stones are precious; but man sees only a few of them... Maurice Maeterlinck
Inclusions in Ruby. The Еxtraordinary Оrdinariness, or Better Never Stop Learning!
Everybody knows what it looks like - mineral pyrite. Bright "metallized" cubes of crystal - very usual part of any mineral collection.. Gemologists in some sense are more lucky - for gemological collection pyrite shows a bit more diverse ...
By studying this stone under the microscope for the first time, all I saw caused a variety of ideas, but that's did not have any about pyrite among all the thoughts! I did not know yet that the pyrite is not even in the form of inclusions, but itself can form rounded nodules and pseudomorphs. I spent long time for the search for an answer to the question - what is it. Mr. Nathan Renfro also saw my photomicrographs and suggested these to be pyrite! I was "smart enough" keep arguing with him for a while! Мr. Renfro also told me which page of Atlas of Inclusion I need to find to see something similar photographed and described. Somehow, shame on me, I missed this illustration within Atlas study.
Later by 3-rd party advanced tests inclusions were confirmed as pyrite! Thank you Nathan for that lesson!
There is below just my thinking and analyzing of what I saw. Due the luck of deep mineralogical knowledge I use mostly chemical logic.
Other inclusions in the stone clearly indicate that the ruby has been subjected to heat treatment. But what this pyrites in current form are telling about? My guess - this stone has not subjected to heating with temperatures sufficient for the diffusion of whatever - whether glass, whether coloring ions - beryllium or lithium. Pyrite is melted at a temperature of 1177-1188 ° C, is not soluble in water under normal conditions, but at high temperatures and higher pressure can quickly corrode and be dispersed by melting while contacting liquid, partially decomposed and partially recrystallized while cooling in the form of brush-like tiny crystals. The photograph shows that the large pyrite "wheels" kept their physical integrity, and there can be seen only a few traces of corrosion (dark spots, containing probably something iron-oxide). Crystals are not even lost their transparency! Their transparency till the last moment did not allow me to agree with the version of the pyrite. But generally in thin layers any solid body can be transparent, this fact is well known .. And these pyrite "wheels", possible (assumption) are formed from ultra-small single crystals, each of which is transparent, and all together still being very thin they are still maybe not fully nut partially transparent.
The surface of one of the "wheel" is covered by dark opaque coating. This "wheel" is contactед with the crack facing surface of the stone. Over the surface of the wheel something same happened as with any ordinary pyrite in the collection happens often as I heard - pyrite does not like contact with oxygen and moisture at the same time... The sulfur is oxidized and released as a gaseous oxide and the iron and nickel remains in the form of a "nondescript" opaque oxides... On the surface of pyrite "wheel" these processes might be accelerated when stone was in stove, or possibly already after faceting because of crack reached facet, during the life of the stone in the faceted form.
If my logic contains any mistake I would be happy to know about this, so no hesitate please with any critic..
I adding pictures again for understanding all this story..
Transmitted light, dark field illumination + Fiber, 80, FoV 2.85 mm
Transmitted light, dark field illumination + Fiber, 120x, FoV 2.00 mm
Transmitted light, dark field illumination + Fiber, 200x, FoV 1.15 mm
Photo4 Transmitted light, dark field, 100x, FoV 2.35 mm
Photo5 Transmitted light, dark field, 200x, FoV 1.15 mm
_________________ All stones are alike, all stones are precious; but man sees only a few of them... Maurice Maeterlinck
These quartzes with inclusions, especially when inclusions are seen as well formed crystals became very expensive! But still it is at least 1 excess "0" in the asking price, and not as starting but ending bid..
_________________ All stones are alike, all stones are precious; but man sees only a few of them... Maurice Maeterlinck
Another small spinel from Sri Lanka, just 0.68 ct, and will be called by almost anyone as crap! But I was lucky to have a chance to look inside, and what I saw I called "Letters of Mother-nature autograph".
Actually color of this stone is weak saturated light reddish-orange, but a few hours spent with camera - and no chance to photograph it with more correct hue... Very stubborn stone!
In the center - dark not-transparent crystal of some heavy mineral, probably uraninite as it is common for pink/red spinels for Ceylon, with its surrounding halos. "Letters" are drawn either by liquid inclusions, or by negative crystals, these objects are too small and details can not be seen...The "stockade" from the elongated square "figures" мost likely - also whether liquid inclusions, оr negative crystals, but how could be formed such "columnar" structures, I have no idea...
Photo: Transmitted light, dark field, 100x, FoV 2,35 mm.
_________________ All stones are alike, all stones are precious; but man sees only a few of them... Maurice Maeterlinck
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