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Posted by Anonymous User  
Anonymous User February 22, 2012 04:05PM
I have this realy dense pitch black xl with a greasy luster from pakistan.

It weighs 53,4 g

It is octahedral in structure

Streak is brownish - olive greenish

The voulme is difficult to estimate because the structure is not a perfect octahedron. Some peaces are missing on one side (maybee 35-25% of the overall volume of perfect octahedron). The sides are 23-26 mm long and by calculating the volume using a formula for octahedral voulme is:

without taking missing part into account ~8 cm3

Taking missing part (35-25%) into account ~5.2 -6 cm3

So density is >8 g/cm3 and <10.23 g/cm3

I am confused that it might be tantalite as that was the name I bought it under. The stone to the left in the streak picture is also supposed to be tantalite but this stone feels much less dense and has a dark brown-black streak (which fitts the description for tantalite better)

OK, I know you're going to say "test it for radioactivity" but I don't have a geigermeter laying around so what else can I do?

Thanks for any help!
open | download - uraninite.jpg (866.5 KB)
Erik Vercammen February 22, 2012 05:38PM
Tapiolite is quadratic (this X may be a dipiramid) and the density is about 8 gram/cubic centimetre.
Reiner Mielke February 22, 2012 05:42PM
Determine the SG as follows: You first weigh the sample. Then you put a large enough container half full of water on a scale and note the weight, then you lower the sample tied to a thin piece of fishing line into the water until it is completely submerged below the water ( if water spills over you need a larger container) and note the new reading on the scale ( the weight of the container of water with the specimen suspended in it). The difference between the two weights is the volume of the specimen. Divide the dry weight of the specimen by the volume and you have the specific gravity ( assuming you use distilled water, there are no air bubbles trapped under the specimen, and the specimen was not touching the sides of the container). Alternatively you can tare the container with water to zero and then the weight you get with the specimen suspended in the water is the volume ( saves you the trouble of taking two readings and subtracting.)
Michael Wood February 22, 2012 06:00PM
Hello Lars,

the crystal looks a bit too shiny for uraninite, which is usually dull, I think. But it does look rather like cassiterite, which is recorded from that part of the world, and cassiterite is quite dense. Just a thought.

Regards, Mike
Anonymous User February 22, 2012 06:03PM
Thanks for the suggestions. Never considered tapiolite nor cassiterite. The x is opaque though and not translucent in any way. What color would you call the streak though? I don't have anything to weigh the sample on which is why I had to resort to geometery. Is it impossible that it could be uraninte?

Edited 1 time(s). Last edit at 02/22/2012 06:09PM by Lars Arvidsson.
Ronald John Gyllenhammer February 22, 2012 07:46PM
Hi Lars,

>"Is it impossible that it could be uraninte?"

It is possible for this to be Uraninite. You said it's greasy, heavy, brown green streak, octahedral, etc. These are all good indications. In the absence of radiation detection equiptment, you should measure the SG (specific gravity) more accurately. Use the method outlined above by Reiner. Also, check with a magnet to rule out Magnetite. Good luck with it.


Edited 1 time(s). Last edit at 02/22/2012 09:56PM by Ronald John Gyllenhammer.
Matt Wall February 22, 2012 09:48PM
Yeah, I agree with Michael Wood, it looks too silvery and shiny for Uraninite or Pitchblende. The best is to test, like you said, with a Geiger counter and check it's radiation.
Hope that helps, Matt.
Anonymous User February 22, 2012 10:03PM
I see.
I will take it with me to the lab I work in and do some density measurements. I'll also bring it to the isotope lab were we have some different kinds of geigermeters and check it there. That should defenately settle the matter, however.... Should this be uraninite.... is it valuable? How much could it catch?
Pavel Kartashov February 24, 2012 01:22AM
Put particle of your stone on zinc plate and drop on it HCl. If in few minutes this particle become light grey and after polishing between fingers become metallic white - it is cassiterite.
I am suppose, that reaction of "tin mirror" will be positive in your case. ;)
Rudy Bolona February 24, 2012 04:06AM
Cassiterite has a light streak white or yellowish. Tapiolite is tetragonal but a lot of its crystals look surprisingly isometric. Remember, Topsham, Maine uraninite is quite lustrous and metallic looking. geiger counter will surely reveal the answer to that. Also tapiolite is opaque and cassiterite is translucent or transparent in small fragments.
Andrew G. Christy February 24, 2012 09:35AM
Another possibility for an octahedral, resinous-adamantine, nearly-black crystal would be a member of the pyrochlore/microlite groups. Needs chemical analysis to stick a species name on it, if so...
António Manuel Ináçio Martins February 24, 2012 10:16AM
Olá me remember a crystal of Microlite.
Pavel Kartashov February 24, 2012 10:06PM
Andrew and Antonio,
this crystal ABSOLUTELY isn't similar to any member of pyrochlore supergroup - crystallographicaly, by lustre, by colour, by streak. And it isn't uraninite of course.
Rudy Bolona February 29, 2012 02:15PM
Hi Lars,

Have you been able to make any determinations on this crystal?

Craig Mercer March 01, 2012 01:16AM
Maybe Spinel Family, Pleonaste. Pakistan as location, could be from anywhere :-S
Matt Wall March 01, 2012 08:14AM
Hi Lars,
If that i pure Uraninite, then you should be getting up towards the $100 mark roughly, depending on the size. =)
Howard Heitner March 05, 2012 01:54AM
Quick test for uranium. Add a drop of nitric acid to a tiny amount of the powder and allow to dry. If U is present, residue will fluoresce green.
Anonymous User March 12, 2012 02:06PM
Ok, I have som updates on the specimen.

It has a SG of 7.053
It is not radioactive
It is not magnetic

My new best guess......Cassiterite

Edited 1 time(s). Last edit at 03/12/2012 02:18PM by Lars Arvidsson.
Alfredo Petrov March 12, 2012 02:19PM
Looks a lot like cassiterite, but the streak is wrong. Did you powder it sufficiently? If cassiterite, the streak should be much paler.
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