Yttrialite "asterism"
Petrick pegmatite, Kingsland Granite Company Quarry, Llano County, Texas, USA
Cross section of a pegmatite boulder that was found to contain a pod of yttrialite in the form of an asterism (right of center). An asterism is a nodule of rare-earth mineral, in this case yttrialite, that is surrounded by a radial fracture pattern due to stresses induced by differences in the coefficients of thermal expansion between the pod and ...
© 2009, Franklin W. Roberts