Explore BrainMass

Pressures for Stable Phases

Calcium carbonate, CaCO_3, has two common crystalline forms, calcite and aragonite.
Calcite, unlike aragonite, is stable at earth's surface. Calculate the pressure (at room temperature) at which the other phase should become stable.

Solution Preview

At roomtemperature and ambient pressure, aragonite is a metastable polymorph of calcium carbonate CaCO3 whose crystallization occurs frequently in nature (shells,corals, mineral sediments, etc.). It transforms into calcite that is the stable polymorphof calcium carbonate when heated. Aragonite is thermodynamically unstable at standard temperature and pressure, and tends to alter to calcite on scales of 107 to 108 years.

Aragonite's more compact structure is composed of triangular carbonate ion groups (CO3), with ...

Solution Summary

315 words show how to find the pressure at which uncommon phases of calcium carbonate become stable.