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I have a cube of pyrite similar to:

enter image description here

(Source: Britannica)

Can pyrite turn into sulfuric acid?

Is this dangerous for me to touch, especially if my hands are sweaty?

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    $\begingroup$ No, pyrite is not dangerous to touch. "Can turn into" is an awfully broad term, it does not mean anything, unless you specify the conditions. Table salt can turn into a poisonous gas (if electrolyzed, that is). Water can turn into an explosive gas. So what? Nothing. $\endgroup$ – Ivan Neretin Nov 9 '16 at 21:28
  • $\begingroup$ Thanks for the response Ivan. Good point. By touch I just mean to play around - roll it around in my hands etc. $\endgroup$ – K-Feldspar Nov 9 '16 at 21:28
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    $\begingroup$ Yes, I got that. No, not dangerous. $\endgroup$ – Ivan Neretin Nov 9 '16 at 21:31
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    $\begingroup$ OK, if you'd wear it like a jewel in constant contact with your skin for years, then maybe it would be somewhat dangerous for the stone. $\endgroup$ – Ivan Neretin Nov 10 '16 at 5:39
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    $\begingroup$ Take it for granite, it's OK. Just don't eat it with St. John's bread, or you'll get pyrites of the carob bean. $\endgroup$ – DrMoishe Pippik Nov 10 '16 at 23:52
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Pyrite does not turn into sulfuric acid. You can burn it with oxygen to give iron oxide and $\ce{SO2}$.

$\ce{4 FeS2 + 11 O2 -> 2Fe2O3 + 8 SO2}$

$\ce{SO2}$ with water gives sulfurous acid. To really get sulfuric acid, $\ce{SO2}$ needs to be oxidised to $\ce{SO3}$ (Contact process), and then reacted with water. Actually with more sulfuric acid to give oleum, which decomposes into two equivalents of sulfuric acid upon dilution with water.

The surface of the pyrite will react very slowly in the acidic conditions in your hand. Very, very slowly. There might be a faint smell of $\ce{H2S}$ recognisable if you handle the pyrite for a while in your sweaty hands.

(Also with water and oxygen from the air, pyrite will slowly react, to finally give sulfuric acid, which will speed up further reaction/degradation. But this typically needs decades of very bad ventilation.)

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  • $\begingroup$ Actually the decomposition of pyrite specimens is a well known problem in the mineral collecting community. It isn't dangerous to the collector, but the specimen can be destroyed. See left hand column on page 2 of the NPS pdf nps.gov/Museum/publications/conserveogram/11-02.pdf $\endgroup$ – MaxW Nov 11 '16 at 5:22
  • $\begingroup$ A nice crystal as shown in the picture above is not likely to be susceptible to decomposition by a bit of humid air, i guess. $\endgroup$ – Karl Nov 11 '16 at 5:33
  • $\begingroup$ You guess wrong... $\endgroup$ – MaxW Nov 11 '16 at 5:40
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    $\begingroup$ @MaxW right, but on what timescale? $\endgroup$ – Karl Nov 11 '16 at 6:00
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    $\begingroup$ Evidently if the pyrite specimen is kept in a very dry case then it will last a very long time. In humid climates perhaps just centuries. The problem became known because museum mineral collections date back over several centuries. $\endgroup$ – MaxW Nov 11 '16 at 14:32
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enter image description here

This is my pyrite right here. I got it from a jeweler. It is not dangerous to handle. However touching to much could cause it to lose its lust and shine. You could polish it with a polish rag to a tool that could remove rust. Again safe to handle just don't handle it to much

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