moonstone

From moon +‎ stone.

• (General American) IPA^(key): /ˈmunˌstoʊn/

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moonstone (countable and uncountable, plural moonstones)

1. (mineralogy) A translucent gemstone, an orthoclase feldspar, that has a pearly lustre.
   • 1922, E[ric] R[ücker] Eddison, The Worm Ouroboros: A Romance, London: Jonathan Cape […], →OCLC, page 3:

     To give light to the presence chamber were seven escarbuncles, great as pumpkins, hung in order down the length of it, and nine fair moonstones standing in order on silver pedestals between the pillars on the dais.

• monotones