Untersuchungen über die Bildungsbedingungen von Quarz im Temperaturbereich zwischen 100° C und 250° C

Heydemann, Annerose

doi:10.1007/bf02652619

Cited by 23 publications

(7 citation statements)

References 19 publications

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“…Experimental results Opal-A Opal-CT -> Silica-K -+ Quartz (2) for the experimental series C. Sequences of (1) and (2) are comparable to those reported by HEYDEMANN (1964) andCARR andFYFE (1958), respectively. However, these sequences, includ ing silica-X and silica-K, have not been observed in natural geological conditions.…”

Section: Introductionsupporting

confidence: 81%

“…Sequence (3) is observed commonly in nature. The fact that sequence (1) and (2) have not been found in nature while sequence (3) is common may be attributed to different physical and chemical conditions (BETTERMANN and LIEBAU, 1975;HEYDEMANN, 1964). Typical X-ray diffractograms of opal-CT show the peaks attributable to low-cristobalite or low-tridymite (Figs.…”

Section: Introductionmentioning

confidence: 99%

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Experimental study on the ordering of opal-CT.

Kano

Taguchi

1982

Geochem. J.

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Hydrothermal experiments treating amorphous silica (opal-A) in an alkaline solution have disclosed. that opal-CT is formed from opal-A or silica-X and is transformed to quartz directly or through silica-K. During the transformation of silica, the d(101) spacing of cristobalite decreases continuously from d(101) _ 4.11 A to 4.05 A, which. suggests a progressive ordering of opal-CT. The decreasing rate of d (101) spacing is approximately expressed by equation (4) given in the text, irrespective of chemical conditions and the transformation sequence of silica. The rate constant is strongly dependent on the reaction temperature but more or less affected by the chemical condition and by the transformation sequence of silica. On the basis of the experimental results, the ordering of opal-CT is discussed in relation to the diagenetic process of siliceous sediments.

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Section: Introductionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Experimental study on the ordering of opal-CT.

Kano

Taguchi

1982

Geochem. J.

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“…Experimental investigations on the formation of quartz from amorphous silica were carried out in alkaline hydrothermal conditions with the addition of alkali metal hydroxides or carbonates [19]. Experiments were carried out over a temperature range of 100 and 250 • C with transformations occurring in a matter of days.…”

Section: -1982mentioning

confidence: 99%

Agate Genesis: A Continuing Enigma

Moxon¹,

Palyanova

2020

Minerals

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This review covers the last 250 years of major scientific contributions on the genesis of agates found in basic igneous host rocks. From 1770 to 1955, the genesis question was frequently limited to discussions based on observations on host rock and agate thick sections. Over the next 25 years, experimental investigations examined phase transformations when silica glass and various forms of amorphous silica were heated to high temperatures. This work demonstrated that the change from the amorphous state into chalcedony was likely to be a multi-stage process. The last 40 years has seen modern scientific instrumentation play a key role in identifying the physical and chemical properties of agate. The outcome of this work has allowed limited evidence-based comment on the conditions of agate formation. There is a general consensus that agates in these basic igneous hosts form at <100 °C. However, the silica source and the nature of the initial deposit remain to be proven.

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“…These transformations have been studied in the field and experimentally by many investigators (White and others, 1956;Carr and Fyfe, 1958;Fyfe and McKay, 1962;Heydemann, 1964;Ernst and Calvert, 1969;Mizutani, 1970;Murata and Nakata, 1974;Murata and Larson, 1975;Murata and Randall, 1975;Kastner and others, 1977;Hein and Scholl, 1978;Keith and Muffler, 1978;Kano and Taguchi, 1982). Time, high temperature, high pH, high salinity, and the presence of dissolved Mg have all been found to favor the transformation of amorphous silica to poorly crystalline cristobalite or opal-CT and then to quartz (or chalcedony).…”

Section: Silicamentioning

confidence: 99%