amethyst vs purpure

amethyst

noun
  • A purple colour. 

  • The tincture purpure, when emblazoning the arms of the English nobility. 

  • A transparent purple variety of quartz, used as a gemstone. 

adj
  • Having a colour similar to that of the gemstone 

purpure

noun
  • purpure 

  • A purple colour on a coat of arms, represented in engraving by diagonal parallel lines 45 degrees clockwise. 

adj
  • In blazon, of the colour purple. 

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