Pencil structure in red siltstone, Red Hills, Tucson Mountains, Arizona


I collected this in the Red Hills in the Tucson Mountains during a mapping project with graduate students.  When I am lecturing on cleavage and linear structures, I like to walk into class with pencil structure in my shirt pocket.  The curviplanar facets on pencils captures my attention, and should invite careful examination to determine how these particular surface shapes evolve.

Age & Formation
Recreation Red Beds formation of Jurassic age, ~170 Ma.