Cerro San Cristobal

This intrusion of about 1.2x0.4 km has a narrow, hornfelsed aureole 15-20 m wide. One rock type consists of 70% nepheline, which is slightly replaced by cancrinite, a little orthoclase and albite, and sparse biotite and sodic amphibole; femics constitute less than 10% of the rock. In boulders derived from the intrusion sodalite has been identified. Numerous boulders of coarse, white calcite rock also occur which contain nests of apatite crystals and an unidentified Zr-Ti silicate. The difficulty of the terrain has, so far, precluded a detailed investigation of the occurrence.