Beryl crystals from Minas Gerais (Brazil), Lumäki (Finland), Sichuan (China), and the Himalayas have been investigated by scanning electron microscopy in order to characterize the shape of etch pits on different crystal faces. The objective was to find out whether etch pits on natural crystals can be used as tools to study provenances and the dissolution process. The crystals were characterized by electron microprobe analysis, infrared spectroscopy, and powder X-ray diffraction. Most of the beryl crystals are normal beryl in the sense that they only slightly deviate from the ideal chemical composition; two crystals, which are also classified as tetrahedrally substituted, show minor substitution of alkalis with Fe2+ for Al. Etch pits are classified as F-type (flat), P-type (pointed), S-type (stepped), H-type (appearing hollow, equal to extremely steep P-type), and C-type (canoe-shaped with curved edges). Different types of etch pits are explained by different defects; F-types occur on point defects, S-types on overlying point defects, P-, H-, and C-types on line defects (dominantly screw dislocations). Different shapes are explained by different dissolution rates in different directions of the crystal. Etch pits were created experimentally at 600 °C, 200 MPa and fluid compositions of 0.5 N NaOH, 0.5 N HCl, 1 N NaCl, and 2 N KCl solutions. Combined results of experiments and the natural crystals show that the dissolution starts by leaching of cations from the channel, followed by the removal of cations from the AlO6 octahedron. The factors that control dissolution of beryl are orientation of the crystal structure (maximum dissolution is perpendicular and parallel to the c axis), crystal defects (inclusions, dislocations), substitution of cations, symmetry of the faces, and chemical composition of the solvents. The morphology of etch pits − rectangular, square, canoe-shaped, rhombic − on the first-order prisms of samples from different localities is significantly different and, if more data will be available in the future, opens the possibility to distinguish their provenance.
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Research Article|
January 01, 2018
Etch pits on beryl as indicators of dissolution behaviour
Raji Kurumathoor;
Raji Kurumathoor
1
Fachgebiet Mineralogie-Petrologie, Technische Universität Berlin
, 10623Berlin, Germany
2
Present address: W/O Ashok Kumar, High Commission of India
, President John Kennedy Street, P.O. Box 162, Port Louis, Mauritius
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Gerhard Franz
1
Fachgebiet Mineralogie-Petrologie, Technische Universität Berlin
, 10623Berlin, Germany
*
Corresponding author, e-mail: gerhard.franz@tu-berlin.de
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Raji Kurumathoor
1
Fachgebiet Mineralogie-Petrologie, Technische Universität Berlin
, 10623Berlin, Germany
2
Present address: W/O Ashok Kumar, High Commission of India
, President John Kennedy Street, P.O. Box 162, Port Louis, Mauritius
*
Corresponding author, e-mail: gerhard.franz@tu-berlin.de
Publisher: Deutsche Mineralogische Gesellschaft, Sociedad Española de Mineralogia, Societá Italiana di Mineralogia e Petrologia, Société Francaise de Minéralogie
Received:
07 Jul 2017
Revision Received:
21 Sep 2017
Accepted:
21 Sep 2017
First Online:
12 Jun 2018
Online ISSN: 1617-4011
Print ISSN: 0935-1221
© 2018 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart
European Journal of Mineralogy (2018) 30 (1): 107–124.
Article history
Received:
07 Jul 2017
Revision Received:
21 Sep 2017
Accepted:
21 Sep 2017
First Online:
12 Jun 2018
Citation
Raji Kurumathoor, Gerhard Franz; Etch pits on beryl as indicators of dissolution behaviour. European Journal of Mineralogy 2018;; 30 (1): 107–124. doi: https://doi.org/10.1127/ejm/2018/0030-2703
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Index Terms/Descriptors
- Asia
- beryl
- Brazil
- characterization
- chemical composition
- China
- crystal dislocations
- crystal structure
- defects
- electron microscopy data
- electron probe data
- etching
- Europe
- experimental studies
- Far East
- Finland
- Himalayas
- hydrothermal conditions
- inclusions
- indicators
- infrared spectra
- leaching
- Minas Gerais Brazil
- mineral surface
- morphology
- pits
- provenance
- ring silicates
- Scandinavia
- SEM data
- Sichuan China
- silicates
- solution
- South America
- spectra
- substitution
- symmetry
- Western Europe
- X-ray diffraction data
- Lumaki Finland
Latitude & Longitude
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