Boulder and Quartz

Boulder noun - A large smooth mass of rock detached from its place of origin.

Quartz and boulder are semantically related. In some cases you can use "Quartz" instead a noun "Boulder".

Quartz noun - A hard glossy mineral consisting of silicon dioxide in crystal form; present in most rocks (especially sandstone and granite); yellow sand is quartz with iron oxide impurities.

Boulder and quartz are semantically related. Sometimes you can use "Boulder" instead a noun "Quartz".