Sapphire vs Gorilla Glass vs mineral: which watch lens survives a decade, and which makers actually say what they use

The three materials

• Sapphire crystal is synthetic corundum, far harder than any glass. Keys, sand and rock do not mark it in normal use. It is brittle by comparison, so a sharp edge strike can chip it, and it costs more, which is why makers put it on top editions and say so.
• Chemically strengthened glass (Corning's Gorilla Glass on the Amazfit T-Rex 3; Garmin's Power Glass on the Instinct 2X Solar) is glass with a compressed surface layer. It flexes and survives impact well, and it scratches under quartz sand, which is most sand.
• Mineral crystal is ordinary hardened glass. Every G-Shock and Pro Trek on this site except the GWG-2000 uses it, as do the Citizen BN0151, Suunto Core Alpha, COROS NOMAD and Luminox 3001 (Luminox gives a hardness of 550 to 650 Vickers). It scratches over years and costs little to replace.

Who names their lens

Scratch vs chip

A scratched lens is a slow death: the watch stays readable for years and gets uglier. A chipped lens is a fast one: it can let water in past the seal. Sapphire trades the slow risk for a small fast one; glass trades the other way. For the buyer this site is written for, who keeps a watch a decade in sand, mud and rock, the slow risk is the one that actually happens, and sapphire wins. The exception is a flat, unprotected lens on a watch that will be dropped onto its face: there, strengthened glass is the safer bet.

The bezel matters as much

The reason a mineral Rangeman is on the toughest watches list is its bezel. A crystal recessed behind a raised bezel takes the strike on the bezel; a crystal flush with a flat case takes it on the glass. Casio's deep resin bezels are why cheap mineral G-Shocks survive decades; the flat square DW-5600E is the most exposed lens Casio makes. Garmin's Instinct has a raised, metal-reinforced bezel around its unnamed lens for the same reason; the fenix pairs sapphire with a titanium bezel and wins both ways.

The picks

How to decide

1. Keeping it ten years in grit? Sapphire, named by the maker. fenix 8, tactix 8, GWG-2000, Vertical, VERTIX 2S, Marathon.
2. Cheap and replaceable? Mineral behind a deep bezel: Rangeman, Mudman, Pro Trek. Accept scratches; the crystal costs less than a strap on some watches.
3. Face-down drops on a flat lens? Strengthened glass: T-Rex 3, Instinct 2X.
4. Maker will not name it? Treat it as glass. Instinct 3 is the example.

The lens is one of three clocks; the other two, power and software, are weighed on buy-it-for-life watches.