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The laws of fluorite and calcite habit formation in terms of the morphogenetic structural-chemical concept

Authors
Journal
Journal of Crystal Growth
0022-0248
Publisher
Elsevier
Publication Date
Identifiers
DOI: 10.1016/s0022-0248(98)01148-8
Keywords
  • Crystal Habit
  • Solution Composition
  • Adsorption
  • Fluorite
  • Calcite
Disciplines
  • Chemistry
  • Earth Science
  • Geography

Abstract

Abstract Effects of solution components, pH, temperature and supersaturation on fluorite and calcite habits (the modern and formerly obtained data) were generalised. Fluorite was synthesised in 40 flux systems (350–1000°C), 7 hydrothermal systems (100–420°C), and about 30 aqueous systems at room temperatures. It is faced mostly by {1 0 0} and {1 1 1}; octahedron as well as rare faces {1 1 0} and {1 1 2} which are displayed preferably at higher temperatures and far from the neutrality. Calcite was synthesised in more than 50 aqueous systems at room temperatures. It is faced mostly by {1 0 1 ̄ 1}+{0 0 0 1}+{0 1 1 ̄ 2} (the cleavage rhombohedron type); strongly alkaline media containing sulphates and citrates cause {0 8 ̄ 8 1}+{0 0 0 1} (the sharpest rhombohedron type). Morphogenetic effectivenesses of the solution components at different conditions were estimated by the comparison of habit variations of these substances. These results were interpreted in terms of the structural-chemical concept of crystal habit formation. In general, the composition and structure of the adsorbed solvent film determining the faceting are deduced from the correlation between the morphodrome and phase diagram features as well as from the epitaxial adsorbate–substrate congruence. Specifically, water adsorbed on fluorite and calcite with help of Ca(OH) 2-layers, is characterised by the dominant morphogenetic effectiveness at the relatively low temperature range close to neutral media, causing cube and pinacoid on these minerals. The appearance of the other faces is connected with destruction of adsorbed Ca(OH) 2 complexes.

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