Dartmoor is one very large pluton of granite however it’s development 270 million years ago has led to some variety to its colours, forms and crystal makeup. Here we have some well developed Feldspar Phenocrysts in a granite mass. This strangley clean surface was found at Calveslake Tor. Each of the white Phenocrysts are approximately 10cm across.
By definition a Phenocryst is; an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock.