It’s naturally occurring, solid, has definite composition, & a repeating crystalline structure. As long as you find it in the wild, it checks every box.
Want it solid at room temperature? Ice VII trapped in diamond.
This one involves impatient swearing about rocks:
Browser the hashtag.
I learned 3 new things in under 5 minutes. Ice shapes landscapes, tracks climate, erupts on icy moons, & whispers secrets of distant worlds.