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Tracy
Joined: 15 Sep 2006
Posts: 551
Location: Toronto
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 Posted: Jun 06, 2010 12:25 Post subject: Re: Sensitivity of sulfides |
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By the way, I forgot to mention that the Geochimica issue has a number of interesting articles about oxidation of sulfides. I downloaded several. Volume 67 No. 5, 2003.
- Tracy
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Jordi Fabre
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Joined: 07 Aug 2006
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Location: Barcelona
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| Posted: Jun 06, 2010 12:36 Post subject: Re: Sensitivity of sulfides |
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By my own experience I never saw specimens of sensitive minerals included in others minerals decayed (of course if the "others minerals" aren't sensitive), including very old specimens from historic collections, so I believe that when them are included, for some reason, them are preserved and them don't decay.
About the Realgar-Pararealgar is very interesting the fact that according Douglass, a Pararealgar return to Realgar if you hot it to a very high temperature (about 300 – 400 Celsius I believe). Unfortunately it seems that although you recover the Realgar species, its previous beauty never return ;-)
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Carles Millan
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| Posted: Jun 06, 2010 14:26 Post subject: Re: Sensitivity of sulfides |
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| Tracy wrote: | | Do I have it right that realgar alters to pararealgar when subjected to light, at about 500 nM wavelength (...). But I'm still confused. Will a transparent/translucent crystal which has inclusions filter out enough radiant energy to prevent the alteration process, or can included crystals alter or degrade anyway? |
Since the visible light spectrum is in the range from 360 nm to about 700 nm, starting with purple color and ending with red, the 500 nm light you are talking about might approximately match the green color, I guess. So a colorless and transparent quartz (or calcite) crystal does NOT filter that wavelength radiation. Otherwise you wouldn't be able to see a green object through it. Indeed, such crystals do not absorb any wavelength radiation in the visible range just because they are transparent and colorless, the opposite being also true.
That said, getting the conclusion that quartz included realgar is not safe might be too much. But there is an argument to think so, provided that the above statement saying that 500 nm radiation is the responsible for the decay of realgar is true. |
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GneissWare
Joined: 07 Mar 2008
Posts: 1287
Location: California
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| Posted: Jun 06, 2010 18:39 Post subject: Re: Sensitivity of sulfides |
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| It also take a fair amount of exposure to complete a transformation. I probably would not keep pyrargyrites and realgars in a sun-filled display case, but if kept in a dimly lit room, and exposed to light occasionally, I suspect little appreciable degradation will occur. I fact, with respect to pyrargyrite, I had a Sampson Mine piece, circa 1850, which still displayed good red color, with minor silvery tarnish. |
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chris
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Joined: 12 Jul 2007
Posts: 538
Location: Grenoble
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| Posted: Jun 07, 2010 09:32 Post subject: Re: Sensitivity of sulfides |
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To complete that, I used to have an orpiment specimen many years ago. It was keep in daylight, but with no direct sunlight. After a few years, it turned yellowish & dust...
Christophe |
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