Uraninite?
19th Nov 2022 18:44 UTCRob Woodside 🌟 Manager
I did the basic testing of the two larger black crystals in this sample, the one of the first photo in this thread with stained aureole and other without stained halo. I knew that checking streak and hardness could damage the small black crystals, as it happened, especially to the soft one, but my curiosity was stronger than the desire to keep them intact. Despite the small size, I was able to perform hardness and scratch tests thanks to its prominent position in the sample. I also checked magnetism using powerful Nd2Fe14B magnets.
The crystal with stained aureole is soft, it scratches gypsum but not calcite and leaves a wide black streak on unglazed porcelain. It is magnetic enough to lift a ∅6x3mm magnet and quenches the fluorescence of both hackmanite and richterite.
The other scratches fluorapatite but not orthoclase and lets only a slight dark gray streak. It is scarcely magnetic, only with a ∅12x10mm magnet floating on water I arrived to detect a slight attraction. It does not have stained aureole, do not quenches fluorescence, rather the contrary, and has a colourless hackmanite halo that is not phosphorescent at all.
Aside these larger crystals, the sample has half a dozen submillimeter black dots scattered on hackmanite, some with stained halo, and a small concentration of black material on stained richterite that cancels out any fluorescence.
So for now we got these facts:
- One black crystal with hardness about 2.5, black streak, considerable magnetism and a stained aureole which quenches fluorescence in both hackmanite and richterite (this one could be an iron mineral partially oxidized but still magnetic).
- Another black crystal, with more metallic appearance, hardness about 5.5, dark gray streak, weakly magnetic, without stained aureole, which do not quenches the fluorescence around it but prevents the phosphorescence (maybe uraninite?).
I've asked a Geiger counter from Santa Claus which I hope will clear up the matter of radioactivity.
Thanks to Rob for rescuing this sample from its retirement in a drawer and inspiring me to study it a little further
Click on photos for comparison mode.
The crystal with stained aureole is soft, it scratches gypsum but not calcite and leaves a wide black streak on unglazed porcelain. It is magnetic enough to lift a ∅6x3mm magnet and quenches the fluorescence of both hackmanite and richterite.
The other scratches fluorapatite but not orthoclase and lets only a slight dark gray streak. It is scarcely magnetic, only with a ∅12x10mm magnet floating on water I arrived to detect a slight attraction. It does not have stained aureole, do not quenches fluorescence, rather the contrary, and has a colourless hackmanite halo that is not phosphorescent at all.
Aside these larger crystals, the sample has half a dozen submillimeter black dots scattered on hackmanite, some with stained halo, and a small concentration of black material on stained richterite that cancels out any fluorescence.
So for now we got these facts:
- One black crystal with hardness about 2.5, black streak, considerable magnetism and a stained aureole which quenches fluorescence in both hackmanite and richterite (this one could be an iron mineral partially oxidized but still magnetic).
- Another black crystal, with more metallic appearance, hardness about 5.5, dark gray streak, weakly magnetic, without stained aureole, which do not quenches the fluorescence around it but prevents the phosphorescence (maybe uraninite?).
I've asked a Geiger counter from Santa Claus which I hope will clear up the matter of radioactivity.
Thanks to Rob for rescuing this sample from its retirement in a drawer and inspiring me to study it a little further
Click on photos for comparison mode.
Here the pics of the hard metallic black crystal.
First photo shows the non-phosphorescent area around the black metallic crystal.
Clik on photos for more views and comparison mode.
Photomicrograph of hackmanite with a metallic black inclusion.
In accord with fluorescence, the colorless halo around the black crystal is also hackmanite, even more fluorescent than the purple one.
Unnamed Richterite occurrence, Ladjuar Medam, Sar-e-Sang, Kuran wa Munjan District, Badakhshan, Afghanistan