Rinsey Cove

The early Permain Tregonning Granite intrudes the Devonian Mylor Slates at Rinsey Cove, a beach near Porthleven. Xenoliths, chiastolite hornfels, a dyke and the contact between the granite and country rocks are all visible in the cliff and wavecut platform. We visit with L6 AS geology students.

My comment on Rinsey Cove at Manonabeach.com.

The white boulders on Rinsey are from the Tregonning-Godolphin granite. The granite is white because of unusual lithium-rich mica, which also made it suitable as an early source of Cornish china clay. The granite was mined on Tregonning Hill for china clay and around Rinsey for tin and copper. The granite outcrops on the eastern and western sides of the cove, forming the headlands. Dark, altered shales, called the Mylor Slate Formation appear in the middle of the cove, providing the colour contrast with the boulders. Granite tends to form rounded boulders because the natural joints are widely spaced and break it into cuboids, which then get rounded by attrition as they roll around and bash into each other. The blocks are also isotropic, equally strong in all directions, with no lines of weakness, so they are hard to split. This geology is distinct from the geology of the Lizard. Take a look at:http://myweb.tiscali.co.uk/geologyofcornwall/rinsey.htm (not my web site) for more information about the geology.