A mineral crystal is one form of hardened glass that is used to shield a watch's dial. Chemically strengthened, mineral crystals are scratch-resistant and very durable to resist normal wear and tear. Compared to sapphire crystals, mineral crystals are less expensive and thus used in most mid-range watches. Mineral crystals are not as hard as sapphire crystals, but mineral crystals do exhibit excellent clarity, along with a reasonable level of resilience to balance cost and performance.