Piles of chert and limestone at the San Antonio quarry. Chert is commonly associated with carbonates of the Edwards Formation. From left to right are Zack Rogers and Eddie Collins from the Bureau of Economic Geology and Michelle Lee from Martin Marietta Materials.


This rock from the Kirschberg member shows “boxwork” structure that results from the original gypsum rock being highly fractured. Fractures were then subsequently filled in with calcite. The gypsum, which was more soluble than the calcite, later dissolved out leaving behind the “boxwork” pattern.