Routine instrumental procedures to characterise the mineralogy of modern and ancient silica sinters

Citation
Nr. Herdianita et al., Routine instrumental procedures to characterise the mineralogy of modern and ancient silica sinters, GEOTHERMICS, 29(1), 2000, pp. 65-81
Citations number
20
Categorie Soggetti
Earth Sciences
Journal title
GEOTHERMICS
ISSN journal
03756505 → ACNP
Volume
29
Issue
1
Year of publication
2000
Pages
65 - 81
Database
ISI
SICI code
0375-6505(200002)29:1<65:RIPTCT>2.0.ZU;2-D
Abstract
Tightly constrained determinative methods can be used to characterise the s ilica minerals (opal-A, opal-CT, opal-C, quartz, moganite) and physical pro perties of silica sinters. Optimal X-ray powder diffraction operating param eters indicate silica lattice order/disorder using untreated. dry, < 106 mu m powders scanned at 0.6 degrees 2 theta/min with a step size of 0.01 degr ees from 10-40 degrees 2 theta and an internal Si standard. Simultaneous di fferential thermal and thermogravimetric analysis of 15.0 +/- 0.1 mg sinter samples of < 106 mu m grain size, at a heating rate of 2 theta degrees C/m in in dry air, identify thermal events associated with dehydration, organic combustion, and changes of state. Where abundant organic matter is present , nitrogen is the preferred atmosphere for thermal analysis. Thermogravimet ric-determined water contents of sinters differ from Penfield determination s reflecting the differing nature of the two techniques. Laser Raman microp robe techniques can be used to explore the mineralogy of particular sinter morphologies and habits down to 10 mu m diameter. The nature of the silica species present can assist in characterising individual sinter deposits and , combined with textural, density and/or porosity determinations, can lead to a better understanding of the hydrology and paleohydrology of a geotherm al prospect. (C) 2000 CNR. Published by Elsevier Science Ltd. All rights re served.