L325 Sandstone, calcareous cement

Portland Group, Shotover Hill, Oxford

Hand Specimen

Pale grey rock, mainly medium to coarse grained quartz sand. Poorly sorted. 
Small amounts of lithic fragments up to 10 mm across, and shell fragments. 
Contains <15 vol% clay, making it an arenite.
Pale grey cement fizzes with acid, indicating that it is carbonate.

Quartz grains, sub-angular to sub-rounded, occasionally rounded, displaying undulose extinction. 
Lithic fragments including flint and quartzite. 
Some grains of feldspar. 
Rare small green clasts. 
Grain supported. 
Cemented by a sparry calcite cement. The cement crystals are large, each enclosing a number of sedimentary grains.

Deposited in an aqueous environment; grains are not rounded enough to have been deposited in an aeolian environment.

The rare green clasts are made up of a cryptocrystalline material, which may be a type of amphibole called glauconite, and some rather decomposed rhyolite or andesite.

Calcareous sandstone
Calcareous arenite