Combined Mineral Class

The CombinedMineral class is a subclass of Mineral that allows combining multiple mineral phases into a single effective phase. This is useful, for example, when there is not enough information to constrain a complete equation of state for a mineral.

The essential idea is to represent the desired mineral as a weighted mechanical mixture of other minerals with well-defined equations of state. In practice, it is usually desirable to combine minerals that are similar in structure and composition to the target mineral. If the composite minerals are picked carefully enough, it may be that only a linear correction to the Gibbs energy of the combined phase (as a function of pressure and temperature) is sufficient to reproduce experimental data for the target mineral.

The CombinedMineral class takes a list of component minerals and their corresponding molar amounts, along with optional energy adjustments, and computes the overall thermodynamic properties self-consistently. The linear adjustments to the Gibbs energy are given in the order: (1) internal energy [J/mol], (2) entropy [J/(mol·K)], and (3) volume [m³/mol]:

from burnman import CombinedMineral

component_minerals = [mineral1, mineral2, mineral3]
molar_amounts = [0.5, 0.3, 0.2]
energy_adjustments = [1000.0, -5.0, 1.e-6]

combined_mineral = CombinedMineral(
    component_minerals,
    molar_amounts,
    energy_adjustments=energy_adjustments
)

In practice, it is usually desirable to combine minerals that are similar in structure and composition to the target mineral. If the composite minerals are picked carefully enough, it may be that only a linear correction to the Gibbs energy of the combined phase (as a function of pressure and temperature) is sufficient to reproduce experimental data for the target mineral. More complex modifications to the Gibbs energy can be achieved by applying Mineral Property Modifiers to one or more of the component minerals.