However, you could use several options depending on the context:
1. Sign for "glass" (with a specific handshape): The sign for "glass" involves making a "C" shape with your dominant hand, then moving it quickly across your palm as if you're breaking glass. This is often used to describe objects made of glass, including crystals.
2. Sign for "rock" + "sparkle" (or "shine"): This combination would convey the idea of a sparkling, crystalline rock. The sign for "rock" is made with a clenched fist, while "sparkle" or "shine" can be signed by moving your fingers in a flickering motion.
3. Sign for "gem" + "specific crystal type" (if known): For specific types of crystals, you can combine the sign for "gem" with the sign for the type of crystal, such as "diamond" or "quartz."
4. Fingerspell "CRYSTAL": If all else fails, you can fingerspell the word "CRYSTAL."
It's important to note that sign language varies depending on the region and community. It's best to consult a local ASL interpreter or resources for the most accurate and culturally appropriate signs.