pyrophane

From pyro- +‎ Ancient Greek φαίνω (phaínō, “I show or shine”).

pyrophane (countable and uncountable, plural pyrophanes)

1. (mineralogy) A mineral which is opaque in its natural state, but is said to change its color and become transparent by heat.

• “pyrophane”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.

• hypnorape