noun
trachyte
A fine-grained volcanic rock; used in geology.
粗面岩は流紋岩の一種で、アルカリ長石を多く含む。
Trachyte is a type of rhyolite and contains abundant alkali feldspar.
The term is composed of 粗 (rough), 面 (surface), and 岩 (rock), describing the rock's typically rough texture. The reading そめんがん is the standard Sino-Japanese reading of these characters.