Mineral Crystal
Mineral crystal is a hardened glass that covers the watch dial. It is far cheaper than sapphire and more resistant to shattering on impact, but it scratches more easily, sitting around 5 on the Mohs hardness scale against sapphire's 9. Seiko's Hardlex is a branded mineral glass.
At a glance
- Hardness
- About 5 on the Mohs scale (sapphire is 9)
- Strength
- Cheap and resistant to shattering on impact
- Weakness
- Scratches more easily than sapphire
Mineral crystal is ordinary glass that has been hardened through heat or chemical treatment. In watchmaking it lands between sapphire and acrylic: harder than acrylic and far cheaper than sapphire, which is why it shows up on most affordable watches.
Strengths and weaknesses
Mineral crystal trades scratch resistance for shatter resistance:
- Upside: it is inexpensive and usually survives a hard knock rather than cracking
- Downside: it scratches easily, rating about 5 on the Mohs scale
The same dial is far better protected by sapphire crystal at Mohs 9, though that raises the cost. We weigh up when each one makes sense in our sapphire vs mineral crystal guide.
Hardlex and branded types
Makers give their own mineral glass recipes a name. Seiko's Hardlex is a well-known example and is common on entry and mid-level models. For how the crystal fits into a watch overall, see the crystal term, and for related material choices, browse the materials section.
Examples
Affordable divers like the Orient Mako typically use mineral crystal, giving durable protection without stretching the budget.
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Comparison
When you choose a watch crystal, the real decision is mineral versus sapphire; each serves a different priority.
| Option A | Option B | Notes |
|---|---|---|
| Mineral crystal | Sapphire crystal | Mineral crystal is cheap and usually survives a knock instead of cracking, but at Mohs 5 it scratches easily. Sapphire crystal resists scratches far better at Mohs 9, though it costs more. |
Related terms
Watches that show this
Frequently asked questions
Is mineral crystal or sapphire crystal better?
It depends on your priority. Mineral crystal is cheaper and more resistant to shattering on impact, but it scratches easily. Sapphire crystal, at Mohs 9, resists scratches far better, though it costs more and can be more brittle.
Does mineral crystal scratch easily?
Yes, it scratches more easily than sapphire. It rates around 5 on the Mohs hardness scale, while sapphire rates 9. In return, mineral crystal tends to survive a hard knock rather than cracking, which is its main advantage.
What is Seiko Hardlex?
Hardlex is Seiko's own branded mineral glass. It is a type of hardened mineral crystal used widely on the brand's entry and mid-level models, sharing mineral crystal's usual balance of low cost and resistance to shattering.