Definition of petrosilex in US English:

petrosilex

noun

Geology
rare
  • Any of various hard, compact, igneous or metamorphic rocks rich in silica; especially (a) hornstone or chert; (b) felsite.

Origin

Late 18th century. From German Petrosilex from petro- + classical Latin silex flint, pebble.

Pronunciation

petrosilex

/ˌpɛtrə(ʊ)ˈsʌɪlɛks/