Vaterite

Formula : CaCO3

Space group: 
Hexagonal - Dihexagonal Dipyramidal HM symbol (6/m 2/m 2/m) Space Group: P 63/mmc
Dana class: 
14.1.2.1V - 14 Anhydrous Carbonates ; 14.1 Anhydrous Carbonates with Simple Formula A+ CO3 ; 14.1.2
High temperature: 
At temperatures below 15C, calcite with six-fold coordination of calcium (by oxygen atoms) was the predominant phase. Vaterite was found to have calcium coordinated to eight oxygen atoms between 25 to 60C. Thermal vibrations probably allowed for an increase in the effective radii of the calcium atoms, allowing stabilisation of the structure. Above 60C aragonite was coordinated to nine oxygen atoms, possibly accounting for its greater stability at these temperatures
Geological context: 
Vaterite is very much less common in nature than the other two forms of calcium carbonate, calcite and aragonite. It has been recorded from calcareous sediments, metamorphic rocks, and meteorites, but most known occurrences are in abnormally calcified tissues, including regenerated damaged mollusc shells, otoliths of some fishes and pathological concretions in man.

Dernière mise à jour le 11.06.2018

THERMODYNAMICS

Individual properties (298.15 K)
M
g·mol-1
cm3·mol-1
ΔGºf
J·mol-1
ΔHºf
J·mol-1
J·mol-1·k-1
CP
J·mol-1·K-1
100.087 37.630 -1125799 -1203300 95.120
Reaction properties

Vaterite + H+ ⇌ HCO3- + Ca+2

298.15 K, 1 bar log10K: 2.43 ΔH°r: -29630 J·mol-1
T(°C) 0 25 60 100 150 200 250 300
log10K 2.89 2.43 1.87 1.32 0.72 0.16 -0.44 -1.17