FMF - Friends of Minerals Forum, discussion and message board

[wade]

During the Christmas holidays I watched the Mineral Perspectives Thumbnails Vol.2, a DVD produced by BlueCap. In the interview with Alex Schauss, a highly respected thumbnail collector, Alex said that being exposed to light realgar can change into opriment which contradict to what I have learned. Does realgar change into pararealgar ? or opriment is the final stable product in this transformation?
I know this might not be a new question, but a clear and correct answer is appreciated.
Happy new year to everyone.

[gemlover]

Early authorities usually described realgar as fading readily, or at least to some degree on exposure to light, and it appears to be less permanent than orpiment. It is said to be incompatible with lead- or copper-containing pigments. Several medieval painting guides do not recommend mixing sulfide pigments with lead white, minium (red lead oxide) or verdigris. It cannot be applied to wet plaster, and hence is not recommended in wet fresco painting techniques. Realgar is synthesized by heating orpiment to a temperature over 150°C or by sublimation of arsenic and sulfur. Although, the manmade mineral closely resembles the color and composition of realgar, it appears to be more susceptible to color change when exposed to light than natural realgar. It can lose its red hue and deteriorate to orange-yellow pararealgar when exposed to light.

The above from an iconofile from Bing search.

John

[Maggie Wilson]

Hi there - from the Handbook of Mineralogy:

Pararealgar is "An alteration product of realgar in stibnite-bearing quartz veins, the alteration
typically a result of exposure to light."

Maggie

[Pete Modreski]

Yes, it's been established that the light-colored alteration product is NOT orpiment, though it looks like orpiment and it's easy to presume it to be that. Pararealgar is I believe what the alteration has been proven to be.

[Peter Megaw]

https://www.minsocam.org/ammin/AM77/AM77_1266.pdf

Here is the full reference on the subject

[Jordi Fabre]

[cascaillou]

I've read that some orpiment samples tend to slowly turn into powder. Do you know what are the compounds formed during this decomposition process?