Crossword Genius

Composition for a learner, but it’s still hard (4)

Ross

I believe the answer is:

opal

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for opal that I've seen before include "Quartz-like gemstone" , "Semi-transparent gem" , "Glassy gemstone" , "Precious stone" , "item in Hatton Garden?" .)

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.