Came across the word 黒曜石［こくようせき］Obsidian.
The use of 曜 had me wondering if it was ateji or if there was a different character before modern reforms. Apparently not. There is another version 黒耀石 using a non jyouyou kanji but this is a modern usage by archeologists.
曜 does have a (original?) sense of shiny but maybe only seen in names and 黒曜石 now.
I always thought it redundant as “day of the week” 曜日

https://ja.m.wikipedia.org/wiki/黒曜石#文化