noun
basalt
A dark, fine-grained volcanic rock. The term is used in geology and everyday contexts.
玄武岩は火山岩の一種です。
Basalt is a type of volcanic rock.
The kanji 玄武 (genbu) refers to the Black Tortoise, a mythological creature associated with the north and the color black, reflecting the rock's typical dark color. 岩 (gan) means rock. The reading is on'yomi.