Roche Rock () stands out as a rocky outcrop some high on the northern flank of the St Austell granite with an approximate area of x .) The rock is of interest to geologists as it is a fine example of quartz
schorl; a fully tourmalinised granite, with black tourmaline crystals. The Rock itself lies approximately north of the northern margin of the St Austell granite, which is the smallest of the five main apophyses of the
Hercynian batholith of Southwest England. The presence of numerous
pegmatites occurring as sheets and containing abundant
miarolitic cavities carrying quartz,
tourmaline,
zinnwaldite,
topaz, and a wide range of other phases, is why the present outcrop of the St Austell granite is considered to have been close to the roof of the intrusion. One such pegmatite was formerly exploited for
orthoclase feldspar at
Tresayes Quarry, on the southern edge of the village and now a geological
nature reserve of
Cornwall Wildlife Trust. Part of this quarry also exploited quartz-tourmaline rock for
aggregate. There is a downloadable geology trail linking Roche Rock to Tresayes Quarry along public
rights-of-way. Roche Rock is considered to be of prime importance for future research, and notification by
Natural England as a geological
SSSI occurred in 1991. On top of Roche Rock is a ruined chapel (dedicated to St Michael) which is said to have been the abode of a
leper or a monk. An 1881 description of the chapel, still had a considerable portion of the masonry standing and one or two windows were fairly perfect, although the steps up to the chapel are roughly cut. Roche Rock has many folk-lore tales associated with it, the two most famous being the legend of
Jan Tregeagle, a 17th-century magistrate, who after death found refuge in the chapel and the other being part of the
Tristan and Iseult tale. Roche Rock was used as a location in the film
Omen III. ==Parish church==