Newly described occurrences of orbicular rock in Precambrian granite, Sandia and Zuni Mountains, New Mexico
— Kathleen A. Affholter and E. E. Lambert

Orbicular rocks are igneous, metamorphic or migmatic features witf orbicules consisting of a core, with one or more concentric shells of contrasted mineralogy or texture, surrounded by matrix (Levenson. 1966). Since their first mention, the unusual structure of orbicular roclks has attracted interest and remains enigmatic. Two occurrences of orbicular rock have been discovered recently in Precambrian exposures in the Sandia and Zuni mountains, New Mexico (fig. 1), and are described in this paper.

 

The Sandia Mountains, east of Albuquerque, are largely composec of the granitic Sandia pluton which hosts at least three orbicular rock occurrences: two previously known exposures near La Luz trail and newly described occurrence in Tijeras Canyon. The Zuni Mountains southwest of Grants, are part of a granitic batholith (Goddard, 1966 which hosts one recently described orbicular occurrence. Petrography wet chemical whole-rock analyses, and mapping are presented for the Tijeras Canyon occurrence (Affholter, 1979); a preliminary descriptior of the Zuni Mountains occurrence is given (Lambert, work in progress)