Crystal Structures as GeobarometersKent Ratajeski
Published Jan. 4, 2005
This exercise is based on the recent formulation of a geobarometer based on the crystal structure of clinopyroxene (Nimis, 1995; 1998; 1999). This method relates structural parameters (e.g., the volumes of the unit cell and the M1 polyhedron) to the pressure at which the mineral crystallizes within basic and ultrabasic magmas.
In this exercise, students are guided into the American Mineralogist Crystal Structure Database to retrieve and download published crystal structure data for viewing in either the CrystalMaker or XtalDraw visualization software packages. The students are instructed on how to examine the structures to determine pressure-sensitive crystallographic parameters and are asked a series of questions related to what they learn.