Area: 1.9 hectare.

Description and Reasons for Notification: 

This locality consists of granite intermediate in character between the two principal varieties of the St Austell granite (Permo-Carboniferous). The rock is texturally similar to the poorly megacrystic zinnwaldite granite, but its chemistry is closer to that of the typical St Austell biotite granite. These features mean that Carn Grey Rock is of critical importance to continuing research aimed at deciphering the relative contributions of magmatic and metasomatic processes in the evolution of the St Austell mass as a whole.