Definition of rhyacolite in US English:

rhyacolite

noun

Mineralogy
rare, historical
  • A feldspar occurring chiefly as white or colourless crystals in volcanic rocks, subsequently identified with sanidine.

Origin

Mid 19th century. From German Ryakolith from ancient Greek ῥυακ-, ῥύαξ mountain-stream, lava-stream + German -o- + -lith, with remodelling of the ending after -lite.

Pronunciation

rhyacolite

/rʌɪˈakəlʌɪt/