uraninite?

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!
/Lars

Tapiolite is quadratic (this X may be a dipiramid) and the density is about 8 gram/cubic centimetre.

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.)

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

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.

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.

Ron



Edited 1 time(s). Last edit at 02/22/2012 09:56PM by Ronald John Gyllenhammer.

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.

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?

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. ;)

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.

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...

Olá....to me remember a crystal of Microlite.
see: [www.mindat.org]

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.

Hi Lars,

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

Rudy

Maybe Spinel Family, Pleonaste. Pakistan as location, could be from anywhere

Hi Lars,
If that i pure Uraninite, then you should be getting up towards the $100 mark roughly, depending on the size. =)

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.

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.

Looks a lot like cassiterite, but the streak is wrong. Did you powder it sufficiently? If cassiterite, the streak should be much paler.