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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Mon Oct 17, 2011 9:19 am 
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http://www.mindat.org/mesg-7-104499.html.
about Poldervaartite and Olmiite.


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Wed Oct 19, 2011 12:30 am 
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Amblygonite is a fluorophosphate mineral, (Li,Na)AlPO4(F,OH), composed of lithium, sodium, aluminium, phosphate, fluoride and hydroxide. Amblygonite's name comes from the Greek words for "blunt angles" in allusion to its variously angled cleavages.

Amblygonite has no less than four different directions of cleavage at different angles from one another and with different qualities of cleavage. Since amblygonite has lithium in its formula, it gives a reliable lithium result with a flame test. Powdered amblygonite which is placed in a gas flame will produce a brightly colored red flame. This is evidence for the presence of lithium.


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Wed Oct 19, 2011 1:14 pm 
Where's the flame colour with respect to that of a strontium flame?


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Fri Oct 21, 2011 7:27 am 
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the color of strontium flame lyes in between the color of lithium flame and the color of calcium flame.

So, you might confuse strontium flame (bright red to crimson red) with calcium (orange to orangish-red / brick red) or lithium (carmine red, more purplish than with strontium).

But you will not confuse lithium with calcium.

Must proceed in complete darkness for better color appreciation, using platinum wire to handle the sample (as steel contaminates the flame with orange color due to incandescent particles).
If you still choose to go for a steel holder (which I suggest you don't), first do a 'blank test' (meaning heating the holder in the flame without the sample) so to appreciate how the steel colors the flame on its own.

Candle flame or lighter flame won't work for flame testing, one need a conical flame from a bunsen burner or blowtorch (a pocket sized alternative is to use a torch lighter producing a conical flame). Inside such flame, one can see that the flame starts with a blue cone, the sample must be heated at the point of this blue cone.

A 2mm sized grain of the mineral is more than enough for testing

Flame testing is usually done one first time with no additives, and then once again but with sample moisted with concentrated hydrochloric acid.

flame testing:
http://en.wikipedia.org/wiki/Flame_test

colored flames (potassium, lithium, strontium, calcium, sodium):
http://scienceamusante.net/wiki/index.p ... lorees.jpg

This being said, flame testing is a destructive mineralogy test which is definately not suitable for gem id, and you can still separate amblygonite-montebrasite from other gems (brazilianite for instance) through optical properties.

For those that can read french, I know of a great book about qualitative chemical analysis of minerals, if you're interested


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Fri Oct 21, 2011 12:12 pm 
You've done that before, haven't you 8) :wink:


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Fri Oct 21, 2011 2:10 pm 
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You've done that before, haven't you

last month (celestite) :mrgreen:

if you need my help, I can burn your diamonds too, for free :twisted:


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Wed Oct 26, 2011 1:04 am 
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Whewellite is a mineral, hydrated calcium oxalate, formula CaC2O4·H2O. Because of its organic content it is thought to have an indirect biological origin and this is supported by it being found in coal and sedimentary nodules. However, it has also been found in hydrothermal deposits where a biological source appears improbable. For this reason it can be classified as true mineral.


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Wed Oct 26, 2011 3:57 am 
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Whewellite is also often found in kidney stones. Organic origin for sure (maybe they can also be formally considered "man made"! :lol: ), but I hope you won't be faceting any of those. :)

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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Wed Oct 26, 2011 4:50 am 
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If you have a whewellite from your kidney, we are happy to facet it for you!


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Mon Nov 21, 2011 1:02 am 
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Sorry guys, we had been offline for a while due to the flood in Bangkok. Had to move out of our house, but now finally back to normal again.

We are quite sure that even no meteorite crater had been found, Libyan Desert Glass is a tektite. It consists of molten sand (silicia), doesn't contain water and might have come into existence by a big meteorite which either passed by very low over the surface or whose impact crater had been covered by desert sand. It is now forbidden to collect Libyan Desert Glass, which could be found in the border area between Egypt and Libya. Interesting what Wikipedia writes about Libyan Desert Glass

The origin of the glass is a controversial issue for the scientific community, with many evolving theories. Meteoritic origins for the glass were long suspected, and recent research linked the glass to impact features, such as zircon-breakdown, vaporized quartz and meteoritic metals, and to an impact crater.[2][3][4][5][6] Some geologists associate the glass not with impact melt ejecta, but with radiative melting from meteoric large aerial bursts. If that were the case, the glass would be analogous to trinitite, which is created from sand exposed to the thermal radiation of a nuclear explosion. The Libyan desert glass has been dated as having formed about 26 million years ago. It was knapped and used as a tool during the Pleistocene Era.

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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Mon Nov 21, 2011 12:10 pm 
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Freakingcat has been selling rare stones for a long time. I remember he was..either the first and/or the only one to offer Painite on ebay for awhile

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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Thu Nov 24, 2011 12:11 am 
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Faceted Dinosaur Bone's from Utah! This is a beautiful example of dinosaur bones. Several gemstone cutters make beautiful cabochons but we decided to facet them. The blue parts of this stone are actually the cells of the dinosaur. This are genuine dinosaur bones which are approximately 350.000.000 years old.


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Thu Nov 24, 2011 12:14 pm 
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The blue parts of this stone are actually the cells of the dinosaur. This are genuine dinosaur bones which are approximately 350.000.000 years old.


Well, a couple of corrections may be in order. Dinosaurs first appeared in the Triassic period (250 to 200 million years ago) following the Permian Extinction. Most of the dinosaur bones I have encountered have been Cretaceous (approx 150-65 million years ago).

Although recent research by Mary Schweitzer discovered blood vessels and structures which looked like whole cells on a microscopic level in a 68 million year old Tyrannosaurus Rex, I believe the orbicular structure in the faceted dinosaur bone pictured above, are not cells, but more likely silicious deposits in bone marrow canals.

Perhaps someone with a stronger background in biology than I can speak to the features more specifically. :)


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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Thu Nov 24, 2011 12:52 pm 
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Wow, Ms. B you are sure well versed in youir fossil knowledge. You are correct on the time line..after that I am lost. Very impressive post

Nice stone freaking cat..that pattern is wicked

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 Post subject: Re: Unusual Gemstone of the Day
PostPosted: Thu Nov 24, 2011 3:43 pm 
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Bone shows highly hierarchical structures, and I've studied smaller features and focused on the mineral part (see Voltolini et al., J. Appl. Cryst. (2011). 44, 928-934 * :P ) so I'm no expert at this scale. But the darker "lines" you see in the bone above should be the trabeculae of a cancellous bone structure. The bluish agate substitutes the bone marrow (plus other stuff, I'm no biologist, and I actually hate living stuff :lol: ) in the volumes between the trabeculae. The haversian canal is a tubular structure at the center of the osteon and it's unlikely to be able to see it with the naked eye, even for a near-sighted person like me. :D

Given that, I'd say that faceting such a beautiful gem bone is a crime (just kidding: don't take my assertion too seriously! :D ). It would have been a stunning cab... :mrgreen: Besides the trabeculae show a strong tendency to overcut: this is I'd say it's unacceptable in faceted stones, but it gives cabs a quite pretty texture. A pretty texture also for knife scales, it makes them feel less "slippery", but smooth at the same time:
Image
(the small 58 mm "knifosaurus")

* Yes, I'm playing the boaster. But you have to wait for the time I'll brag about my co-authored paper on the Journal of Food Science (I'm a geologist). I do that all the time at the cafe' with my colleagues: "Shut up you guys! You know I'm formally qualified to say that this coffee definitely sucks!" :lol:

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