The Gatesburg Formation (State College, Pennsylvania) is a light gray silliceous oolite cemented by a light gray compact silica (chalcedony). Oolite is here used as a rock name, but the term also refers to the small spherical grains that can be seen (about 1 mm in diameter). The oolites were probably originally made of calcite but are now made of chalcedony. This sample is 10 cm wide.