Calcite growth rate

Figure 7. Langmuir isotherm plot of ko/(T o — k) against the reciprocal of the phosphate concentration, where ko is the calcite growth rate constant in the absence of phosphate and k is the rate constant in the presence of phosphate ( ) ko = 0.824 (n)ko = 1.205 (O)ko = 0.790. Adapted from Ref. 43.

Figure 2. Effects of different parameters on cave calcite growth rate A) precipitation rates for vmious film thicknesses (d in cm die thicker line represents average film thickness of 7.5 cm Baker and Smart, 1995) as a function of [Ca ] in the water film (T = 10°C, cavepCOz = 3x10" atm) B) precipitation rates (widi d = 0.01 cm and cave pCOt = SxlO atm) for various temperatures (in °C) C) precipitation rates for various cave pC02 levels (in 10 atm) (d = 0.005 cm, T = 10°C) D) values of the kinetic constant a as a function of temperature for different film diicknesses (d in cm)(cavepCO = 3x10 atm). All figures after B er et al. (1998).

Figure 4-6 Interface reaction rate as a function of temperature, pressure, and composition. The vertical dashed line indicates the equilibrium condition (growth rate is zero), (a) Diopside growth and melting in its own melt as a function of temperature with the following parameters Te= 1664K at 0.1 MPa, A5m-c = 82.76J mol K , E/R —30000 K, 4 = 12.8 ms K, and AV c l. l x 10 m /mol. The dots are experimental data on diopside melting (Kuo and Kirkpatrick, 1985). (b) Diopside growth and melting in its own melt as a function of pressure at 1810 K (Tg = 1810 K at 1 GPa from the equilibrium temperature at 0.1 MPa and the Clapeyron slope for diopside). (c) Calcite growth and dissolution rate in water at 25 °C as a function of Ca " and CO concentrations.

Because one mole of calcite reacts with one mole of quartz, the molar reaction rates of phase A and B are identical, which equals the molar growth rate of wollastonite (D). Therefore, the linear reaction rate and u are related as follows ... 

Chemisorption raises basic questions for the carbonate geochemist about the boundary between sorption and coprecipitation. If the adsorption reaction takes place in a solution that is also supersaturated with respect to the carbonate mineral substrate, then the adsorbed ions can be buried in the growing layers of the mineral and become coprecipitates. This mechanism can result in distribution coefficients that are dependent on growth rates. Also, when chemisorption is involved, an entirely new phase or a coprecipitate can form in the near-surface region of the carbonate (e.g., see Morse, 1986 Davis et al 1987). A classic example is apatite formation on calcite in dilute solutions (e.g., Stumm and Leckie, 1970). 

One of the most controversial topics in the recent literature, with regard to partition coefficients in carbonates, has been the effect of precipitation rates on values of the partition coefficients. The fact that partition coefficients can be substantially influenced by crystal growth rates has been well established for years in the chemical literature, and interesting models have been produced to explain experimental observations (e.g., for a simple summary see Ohara and Reid, 1973). The two basic modes of control postulated involve mass transport properties and surface reaction kinetics. Without getting into detailed theory, it is perhaps sufficient to point out that kinetic influences can cause both increases and decreases in partition coefficients. At high rates of precipitation, there is even a chance for the physical process of occlusion of adsorbates to occur. In summary, there is no reason to expect that partition coefficients in calcite should not be precipitation rate dependent. Two major questions are (1) how sensitive to reaction rate are the partition coefficients of interest and (2) will this variation of partition coefficients with rate be of significance to important natural processes Unless the first question is acceptably answered, it will obviously be difficult to deal with the second question. 

The rate of reaction is dependent on the nucleation and growth rates of calcite, not the dissolution rate of aragonite. Curiously, it has also been observed that absolute rates are strongly dependent on the aragonitic material used. This observation appears to contradict the generally held conclusion that rates are strictly dependent on calcite nucleation and precipitation rates, not the dissolution rate of aragonite. 

Figure 7.18. A) Rate of calcite growth (Vg) as a function of supersaturation. B) Rate of calcite growth as a function of temperature. (After Wollast, 1971.)...

Mucci A. and Morse J.W. (1983) The incorporation of Mg2+ and Sr2+ into calcite overgrowths influences of growth rate and solution composition. Geochim. Cosmochim. Acta 47, 217-233. 

Teng H. H., Dove P. M., and DeYoreo J. J. (2000) Kinetics of calcite growth surface processes and relationships to macroscopic rate laws. Geochim. Cosmochim. Acta 64, 2255-2266. 

Figure 10. Theoretical growth rates of calcite from tiiin water films. Contours are CO 2 partial pressures in units of 10 atm. Adapted from Baker et al. (1998).

In speleothem and other inorganic calcite work, both sample size and precision are related to the error in age (Ludwig et al., 1992). Deposition rates of speleothems are often low, so that large sub-samples will integrate large time intervals and introduce error in age if uranium concentrations and growth rates are not constant in that interval. On the... 

Growth rate of mammillary calcite ranges from about 0.3 to 1.3 mm/1,000 years (Ludwig et al., 1992 Plummer et al., 2000). 

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