The role of dislocations and surface morphology in calcite dissolution

Journal Article · Sat Feb 29 23:00:00 EST 1992 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(92)90049-O· OSTI ID:5077640

MacInnis, I N; Brantley, S L ^[1]

---

1. Pennsylvania State Univ., University Park (United States)

The authors have measured the dissolution rate for undeformed ({rho} {approximately} 10{sup 3} dislocations{center dot}cm{sup {minus}2}) calcite to be 3.1 {times} 10{sup {minus}10} mol{center dot}cm{sup {minus}2}{center dot}s{sup {minus}1} in free-drift rotating disk experiments at 1,160 rpm, 25C and pH 8.6 in 0.7 M KCl solution far from equilibrium. The rate increased by a factor of {approximately} 2.3 for a strained sample ({rho} = 6 {times} 10{sup 8}{center dot}cm{sup {minus}2}). Dissolution rates of calcite far from equilibrium were observed to depend on surface preparation and surface morphology resulting from defects outcropping at the crystal surface. The high dissolution rate for mechanically polished surfaces is attributed to enhanced dissolution at cracks and dislocation loops produced in the grinding process. The initial dissolution rate for cleaved surfaces depends on the surface morphology, but reaches a reproducible steady state value when a constant bimodal size distribution of intersecting pits with time-independent wall slope is achieved. The two populations of etch pits consist of abundant, short-lived, small etch pits (attributed to nucleation at impurity or point defect clusters) and long-lived, larger point-bottomed pits (attributed to dislocations). Consistent with this interpretation, significant dissolution at an abundance of nondislocation nucleation sites in undeformed calcite explains the relatively small increase in dissolution rate for strained samples. Simulation of bulk crystal dissolution based on etch pit growth rates is in reasonable agreement with observed dissolution rates and surface morphology. Activation energies for pit deepening and widening were measured between 5 and 50C as 27 {plus minus} 5 and 37 {plus minus} 3 kJ mol, respectively. These values are lower than the measured activation energy for bulk dissolution (59 {plus minus} 12 kJ mol).

• OSTI ID: 5077640
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 56:3; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
152003* -- Geothermal Data & Theory-- Rock-Water-Gas Interactions
36 MATERIALS SCIENCE
360602 -- Other Materials-- Structure & Phase Studies
58 GEOSCIENCES
580000 -- Geosciences
ACTIVATION ENERGY
ALKALI METAL COMPOUNDS
AQUEOUS SOLUTIONS
CALCITE
CARBONATE MINERALS
CHLORIDES
CHLORINE COMPOUNDS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DATA
DISLOCATIONS
DISPERSIONS
DISSOLUTION
ELECTRON MICROSCOPY
ENERGY
EXPERIMENTAL DATA
HALIDES
HALOGEN COMPOUNDS
INFORMATION
KINETICS
LINE DEFECTS
MICROSCOPY
MINERALS
MIXTURES
MORPHOLOGY
NUMERICAL DATA
PH VALUE
PHOTOGRAPHY
PHOTOMICROGRAPHY
POTASSIUM CHLORIDES
POTASSIUM COMPOUNDS
SOLUTIONS
SOLVENT PROPERTIES
SURFACE PROPERTIES
TEMPERATURE RANGE
TEMPERATURE RANGE 0273-0400 K
TRANSMISSION ELECTRON MICROSCOPY