boulder, rock, cliff
岩 centers on large, solid masses of stone: a boulder, a rock, or a rocky cliff. The idea is a prominent, often imposing, natural stone formation.
岩 combines 山 (mountain) and 石 (stone) to depict a rocky mountain or boulder. This is a straightforward semantic compound.
A mountain 山 made of stone 石 is a giant boulder or rocky cliff. Picture a massive rock face rising like a mountain.
For ガン, imagine a gun made of solid rock: gun -> ガン, and the boulder is as hard as a gun's metal.
rock; boulder
Iwate (prefecture)
lava
Iwanami (publisher)
bedrock
Iwanami Kokugo Jiten (Japanese dictionary published by Iwanami Shoten) (abbr)
rock
rocky mountain
rocky area; rocky tract; rocky stretch (of a climb); wall (of rock)
halite; rock salt
char (esp. the Japanese char, Salvelinus pluvius); charr
granite
Iwanami Shoten, Publishers (publisher)
limestone
reef
cavern; grotto
monolith; large slab of rock
among rocks
rock door (to a cave)
cave; cavern