Opals from Slovakia ("Hungarian" opals): a re-assessment of the conditions of formation

Research areas:

• Surfaces planétaires (2011 - 2016)

Year:

2004

Authors:

• Benjamin Rondeau
• E Fritsch
• M Guiraud
• C Renac

Journal:

EUROPEAN JOURNAL OF MINERALOGY

Volume:

16

Number:

5

Pages:

789-799

Month:

SEP-OCT

ISSN:

0935-1221

BibTex:

@article{WOS:000224571200008, author = "Benjamin Rondeau and E Fritsch and M Guiraud and C Renac", abstract = "Slovakian opals are found in an andesitic host-rock and believed to have formed by water circulation during a tectonic event. Their physical properties are investigated: X-Ray Diffraction (opal-A), Raman spectra (main Raman peak at 437 cm(-1)) and microstructure (large silica spheres 125 to 270 nm in diameter) surprisingly are properties of opals usually found in sedimentary deposits, and differ from those of opals found in other volcanic deposits. The temperature is proposed to control these physical properties rather than the nature of the host-rock. Some preliminary results of oxygen isotopic composition indicate a high 6180 for Slovakian and Australian opals (approximate to 31 parts per thousand) consistent with low temperatures of formation (lower than 45 degreesC; by contrast, Mexican opals-CT show a lower delta(18)O at 13 parts per thousand consistent with a formation at a higher temperature, possibly up to 190 degreesC.", doi = "10.1127/0935-1221/2004/0016-0789", extra = "PICL", issn = "0935-1221", journal = "EUROPEAN JOURNAL OF MINERALOGY", month = "SEP-OCT", number = "5", pages = "789-799", title = "{O}pals from {S}lovakia ({\&}quot;{H}ungarian{\&}quot; opals): a re-assessment of the conditions of formation", volume = "16", year = "2004", }

Abstract:

Slovakian opals are found in an andesitic host-rock and believed to have
formed by water circulation during a tectonic event. Their physical
properties are investigated: X-Ray Diffraction (opal-A), Raman spectra
(main Raman peak at 437 cm(-1)) and microstructure (large silica spheres
125 to 270 nm in diameter) surprisingly are properties of opals usually
found in sedimentary deposits, and differ from those of opals found in
other volcanic deposits. The temperature is proposed to control these
physical properties rather than the nature of the host-rock. Some
preliminary results of oxygen isotopic composition indicate a high 6180
for Slovakian and Australian opals (approximate to 31 parts per
thousand) consistent with low temperatures of formation (lower than 45
degreesC; by contrast, Mexican opals-CT show a lower delta(18)O at 13
parts per thousand consistent with a formation at a higher temperature,
possibly up to 190 degreesC.