Dark, Shiny Volcanic Glass
This page is the CodyCross answer for the clue below from Futuristic City , Group 999, Puzzle 4 (Sustainable Aviation Fuel).
Question is: Dark, Shiny Volcanic Glass
and the answer is: OBSIDIAN
Word Meaning:
OBSIDIAN — (mineralogy) A type of naturally occurring black glass produced by volcanoes.
Definitions from Wiktionary.