amethyst vs heliotrope

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 

heliotrope

noun
  • A light purple or violet colour. 

  • Particularly, a purple-flowered plant of the species Heliotropium arborescens. 

  • A bloodstone (a variety of quartz). 

  • An instrument, employed in triangulation, that uses a mirror to reflect sunlight toward another, very distant, surveyor. 

  • The fragrance of heliotrope flowers. 

  • A plant that turns so that it faces the sun. 

adj
  • Light purple or violet. 

  • Keeping one’s face turned toward the sun. 

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