Is a sapphire crystal on a watch the same thing as a sapphire gem?

Many high end watches (or even middle-end watches) advertise that the crystal is sapphire on the watch. The reason being is sapphire has a super high hardness only beat by diamond (maybe there are some other things harder but it is used because it is exceptionally hard). Hardness means less likely to be scratched so this is a desirable trait.

But when they say your watch has a sapphire crystal is that the same thing as a sapphire gem?

It’s synthetic but the same like synthetic diamond is the same as natural diamond - in other words chemically the same as a pure gem and has the same crystal structure but without the imperfections and impurities



I thought this was going to be about jewel bearings, but the answer is the same as zoid gave.

Does “watch crystal” have more than one meaning? (I really do not know)

It generally refers to the transparent material covering the face of the watch. Watch crystal Definition & Meaning - Merriam-Webster

However, watch crystal could refer to the quartz piezoelectric crystal that keeps time in a quartz electronic watch ‘movement.’ Watch crystals

And what MrDibble is talking about are jewel bearings, which utilize rubies and sapphires to minimize friction. Predominantly used in mechanical watch movements.

Note that, while sapphire is often thought of as blue, the color is due to impurities, and pure sapphire is colorless. Depending on the impurities, sapphire can be any color other than red, and the only reason it can’t be red is because if it is, then it gets called “ruby” instead.

It’s also possible to have various sorts of crystalline defects. One sort of defect results in star sapphires, which are among the most valuable of gems. So both defects and impurities can improve a gem’s value.

The same substance is also sometimes known as “corundum”, “emery”, or “alumina”, depending on context (those names are more often used in industrial or laboratory contexts, not jewelry).

While the substances you list are chemical components wise the same, the crystal structures are different leading to different melting points, hardness, etc etc. Alumina is prolific when it comes to crystal structures.

If they can make watch crystals out of sapphire why not cell phone screens?

The little I looked up on this said sapphire beats Gorilla Glass for hardness.

Looking at some watch crystals it seems there is as much material there as on a cell phone screen (smaller area but thicker).

It does. But Mohs hardness isn’t be the be-all end-all for durability. Dynamic toughness is also desired, and sapphire may not be as durable as tempered glass versus that stress. See, e.g, this Cnet story about Corning testing their Gorilla Glass vs artificial sapphire. I guess artificial sapphire cell phone screens have been around for some time though. This article talks about HTC having a phone in 2017 with one.

Hard substances tend to be brittle. In a small object like a watch crystal, it’s not much of an issue, but a larger object like a phone screen needs a bit of flexibility.

am77494, what I’m reading online says that sapphire and ruby are the names used for corundum when it’s used as a gem, emery is a mixture of corundum and other minerals, and alumina is the general term for all of the different crystalline forms of Al[sub]2[/sub]O[sub]3[/sub].

In other words, corundum, sapphire, and ruby are all the same substance, emery is mostly the same substance, and alumina can be the same substance.

You can still scratch a sapphire crystal.
My buddy and I have Garmin Fenix 5X watches, which have sapphire crystals. We both wore them on the last Spartan race, and his finished with a big scratch on it.

It’s been done. But a sapphire crystal large enough for a smartphone screen is very expensive. And as others noted, hardness is not the same thing as strength, and Gorilla Glass is stronger than sapphire.

Are you sure it’s a scratch, and not the edge of a crack?

But I suppose it’s possible that he accidentally rubbed up against someone’s wedding ring.

Fully agree Chronos. I was only referring to alumina in particular and could have been more specific.

I remember from undergraduate ChemE classes that one form of alumina is highly detrimental to the aluminum extraction in molten cryolite cell.

Also Alumina is very commonly used as a catalyst or a catalyst support in reactors. And only gamma alumina provides good catalyst performance and other forms don’t.

I’ve worked with sapphire as a component of the instruments I design. Specifically, it’s commonly used for pistons[sup]1[/sup] in the very-high-pressure pumps used for chemical analysis.

One thing to keep in mind is that while sapphire is very hard and fairly strong, its material properties depend on direction—it’s anisotropic. Anisotropy means that sapphire can be significantly more vulnerable to certain impacts than glass is.

(Wood is also anisotropic—it’s strongest in the direction of the grain).

[sup]1[/sup] I’ve always thought “sapphire piston” would be a great band name.

Sounds more like a porn name.

The iPhone screens almost were back in 2014.

What do you mean by “stronger”?

Pretty sure sapphire is harder than Gorilla Glass but I get that hardness is not the only measure of how strong something is.

I’ve seen it said that Gorilla Glass is “comparable” to sapphire in hardness but I am guessing if it was harder they’d sing it from the rooftops.