PACS 64.30.+t, 65.40.De A particularly simple two-parameter relation for the variation of the product of bulk modulus and volume thermal expansion coefficient of solids with changing temperature has been found. The relation, although empirical, fits all minerals tested. We used this relation for the isobaric equation of state and compared with other equations of state. The excellent results show that it can be successfully applied to study the temperature behavior of minerals from room temperature to high temperature.