Mineral Crystal
Mineral crystal is a hardened glass fitted over the watch dial. It is far cheaper than sapphire and more resistant to shattering on impact, yet it scratches more readily, rating 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 readily than sapphire
Mineral crystal is ordinary glass that has been hardened through heat or chemical treatment. In watchmaking it sits between sapphire and acrylic: harder than acrylic and far cheaper than sapphire, which is why it appears 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 readily, rating about 5 on the Mohs scale
The same dial is far better protected by sapphire crystal at Mohs 9, although that pushes up 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 as a whole, see the crystal term, and for related material choices, browse the materials section.
Examples
Affordable divers such as 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 rather than cracking, but at Mohs 5 it scratches readily. Sapphire crystal resists scratches far better at Mohs 9, although 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 readily. Sapphire crystal, at Mohs 9, resists scratches far better, although it costs more and can be more brittle.
Does mineral crystal scratch easily?
Yes, it scratches more readily than sapphire. It rates around 5 on the Mohs hardness scale, whereas 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.