nacreous vs opalescent

nacreous

adj
  • Exhibiting lustrous or rainbow-like colors. 

  • Of, or resembling nacre (mother of pearl). 

opalescent

adj
  • Exhibiting a milky iridescence like that of an opal. 

How often have the words nacreous and opalescent occurred in a corpus of books? (source: Google Ngram Viewer )