Pea Grit is the name given to a limestone rock type that is characterised by large spherical grains or pisoids. Pisolite is a sedimentary rock made of pisoids, which are concretionary grains, typically of calcium carbonate but sometimes of other minerals. The pea like grains are approximately spherical and have concentric layers. The pisolite name derives from the Hellenic word for pea.
Pisolites have formed by chemical precipitation. Pisolites form by the precipitation of calcium carbonate around nucleation site trapped in sediment within the calcium rich water table zone of soils or marine tidal flats. Pure calcium carbonate pisoids are white. The presence of other elements will colour the pisoids, iron - red/brown, manganese - grey/black. Pisoids have been observed in Martian soils and are considered evidence of a once wet Mars.
In Hallett Cove the lower geology is overlaid by a hard calcrete cap. As you walk along the path from the listed coordinates to the reference location at the top of the stairs you will see an extensive numbers of pisolites. Take some time to examine the pebbles and the exposed pisoids in the limestone at the reference locaton. There are two earthscience tasks and an optional task to answer. Send this information in an email or message to the cache owner. You can log immediately but do not forget to send your answers. Don't forget to admire the view.
Please send your answers for the following questions.
-What is the typical size of the pisoids? Are they even size? Are they bigger than peas?
-What is the common internal colour of the pisoids? What other internal colour do you see? Why?
-(Optional) Did you seen any martians?
Pea Grit on Mars
Pea Grit on Earth