We all know that Dartmoor is a large granite pluton forming an area of highland in the south west. This rather large igneous pluton exists as part of a much larger batholith that sits deep under the south west counties peninsular, linking areas such as Bodmin Moor , West Penwith and the Isles of Scilly.
The dominance of this huge granite node Dartmoor can easily draw one’s attention from the other rocks that are associated with Dartmoors scenery. The emplacement of such a large body of granite could not have happened without a few adjustments. These changes to the rock types on Dartmoor can be subtle but they can be spotted with practice.
If you know your rocks then a visit to White Tor SX 542786 and Boulters Tor SX 525780 on the west of Dartmoor will reveal a darker stone than the usual pale grey rounded Dartmoor boulders. The boulders at White Tor are dark grey, mottled and blockier, with sharper fractures than the more rounded edges of weathered granite boulders. Take a closer look and then you’ll see that there is a distinct lack of quartz to the crystal make-up and the minerals are all-together darker (greeny to black). The British Geological Survey suggest a coarse grained Gabbro, as related to Basaltic lava but cooled slowly to make a coarse-grained texture. The mottled appearance that is given the face of some boulders inset. helps reveal one of the differences from that of your more usual granite boulders.
Keep you eyes peeled, not all Dartmoor granite…is granite!