Quick
Search: 		  
advanced search
 GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help 
American Mineralogist Don't get GSW? Talk to your librarian.
JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
American Mineralogist; August 2006; v. 91; no. 8-9; p. 1323-1330; DOI: 10.2138/am.2006.2165
© 2006 Mineralogical Society of America
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Bonazzi, P.
Right arrow Articles by Menchetti, S.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation

Light-induced changes in molecular arsenic sulfides: State of the art and new evidence by single-crystal X-ray diffraction

Paola Bonazzi*, Luca Bindi, Giovanni Pratesi and Silvio Menchetti

Dipartimento di Scienze della Terra, Università di Firenze, via La Pira 4, I-50121 Firenze, Italy

Correspondence: * E-mail: pbcry{at}geo.unifi.it

Light-induced structural changes in single crystals belonging to the ß-As4S4-As8S9 series and in a crystal of synthetic ß-As4S3 were monitored step by step by determining the unit-cell dimensions. A marked increase of unit-cell volume as a function of exposure time was observed for all the crystals belonging to the ß-As4S4-As8S9 series except for stoichiometric alacranite (As8S9). No significant change upon long exposures to light was observed for the synthetic ß-As4S3 crystal. Crystal structure refinements were carried out for crystals with different composition at selected steps of the light-induced process. The structural results clearly showed that the percentage of the As4S5 molecule in the structure increases when a crystal is exposed to light. Therefore, the increment of the unit-cell volume induced by light exposure appears to be related to a random replacement of As4S5 for As4S4 in the structure according to the reaction 5As4S4 + 3O2 -> 4As4S5 + 2As2O3. The results obtained in the present study combined with a critical review of data previously published indicate that the As4S4 molecule is able to incorporate sulfur to convert to As4S5 upon exposure to light, whereas either As4S3 or As4S5 molecules do not go undergo any modification. It appears that the extent of sulfur incorporation is strictly controlled by the type of molecular packing as well as by the kind of molecule.

A final, complete conversion to pararealgar was observed only for pure ß-As4S4, whereas non-stoichiometric As8S9–x crystals initially containing variable amounts of ß-As4S4 microdomains convert only partially to pararealgar upon light exposure.

Key Words: XRD data • arsenic sulfides • crystal structure • light-induced alteration • alacranite • ß-As4S4




This article has been cited by other articles:


Home page
 American MineralogistHome page
A. Kyono
Molecular conformation and anion configuration variations for As4S4 and As4Se4 in an anion-substituted solid solution
American Mineralogist, April 1, 2009; 94(4): 451 - 460.
[Abstract] [Full Text] [PDF]

Home page
 American MineralogistHome page
L. Bindi and P. Bonazzi
Light-induced alteration of arsenic sulfides: A new product with an orthorhombic crystal structure
American Mineralogist, April 1, 2007; 92(4): 617 - 620.
[Abstract] [Full Text] [PDF]


JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 2009 by Mineralogical Society of America