Mineral-crystal watches

Mineral crystal is hardened glass — typically tempered, sometimes laminated — and sits between acrylic and sapphire on both hardness (Vickers ~500) and shatter resistance. It is the convention for entry-tier watches under $300: most Casio analogs, lower-tier Seiko 5 references, and many Citizen Eco-Drive watches. Mineral scratches more visibly than sapphire and does not polish as cleanly as acrylic. Almost no luxury or even mid-tier reference still uses mineral crystal as standard.