The Collaborative International Dictionary
Growan
Growan \Grow"an\, n. [Cf. Arm. grouan gravel, Corn. grow gravel, sand.] (Mining.) A decomposed granite, forming a mass of gravel, as in tin lodes in Cornwall.
Wiktionary
growan
n. (context UK mining English) A decomposed granite, forming a mass of gravel, as in tin lodes in Cornwall.