Sapphire, mineral and acrylic watch crystals compared
Sapphire is the most scratch resistant and the most expensive, mineral glass is the everyday compromise, and acrylic is the softest but the only one you can polish scratches out of at home. Sapphire is worth paying for on a watch you will wear daily. On a watch that lives in a box, it changes very little.
| Crystal | Hardness | Scratches | Shatters |
|---|---|---|---|
| Sapphire | Mohs 9 | Almost never | More readily than mineral |
| Hardlex | Mohs 6 to 7 | Occasionally | Rarely |
| Mineral | Mohs 5 to 6 | Readily | Rarely |
| Acrylic | Mohs 3 | Constantly | Never — it cracks or crazes |
Hardness is not toughness
These are two different properties and confusing them is the most common mistake made about watch glass. Hardness is resistance to scratching. Toughness is resistance to breaking. Sapphire is far harder than mineral glass and slightly more brittle.
In practice that trade is worth taking. Scratches accumulate from ordinary daily contact with door frames and desks. Impacts hard enough to break a crystal are rare. But it explains why some tool watches and most military-issue pieces still use mineral or acrylic: a crystal that crazes and stays in place is safer than one that shatters.
Sapphire and glare
Sapphire is more reflective than mineral glass, so an uncoated sapphire crystal can be noticeably harder to read in bright light. Manufacturers address this with anti-reflective coating, applied either to the underside only or to both faces.
Coating on both faces gives the near-invisible glass effect, but the outer layer is soft and scratches — so the crystal underneath stays perfect while the coating develops marks. Underside-only coating is the more durable choice and the more common one.
What Hardlex actually is
Hardlex is Seiko's proprietary hardened mineral glass. It sits between ordinary mineral and sapphire: noticeably more scratch resistant than standard mineral, not in sapphire's league, and considerably cheaper to produce.
Other manufacturers have equivalents under their own names. Treat any branded hardened glass as an upgrade on mineral rather than an alternative to sapphire.
Why acrylic still exists
Acrylic scratches if you look at it wrong. It is also the only crystal an owner can restore themselves — a few minutes with a polishing compound removes light scratches completely, which is not possible with either mineral or sapphire.
It gives a warm, slightly distorted look through the domed profile that a lot of people prefer on vintage-styled watches, and it is genuinely shatterproof. On a reissue or a field watch it is often a deliberate choice rather than a cost saving.
Common misconceptions
Sapphire is unbreakable.
It is unscratchable in normal use, not unbreakable. It is more brittle than mineral glass and a sharp knock on a hard edge can crack it.
Sapphire coated means sapphire.
Sapphire coated is mineral glass with a thin hard layer applied. The layer wears through and the glass underneath scratches normally. It is not the same product.
A scratched crystal has to be replaced.
On acrylic, no — it polishes out. On mineral, replacement is usually cheaper than attempting a polish. On sapphire it rarely arises.
Crystals across the watches we list
Crystal type is recorded on nearly every watch on the site. The split below shows what the market actually offers at each level.
| Crystal | Watches | From |
|---|---|---|
| Sapphire | 2,690 | £27.49 |
| Hardlex | 116 | £125 |
| Mineral | 2,713 | £14.99 |
| Acrylic | 106 | £24.90 |
Based on 5,676 watches listed and in stock. Updated continuously.