How were diamonds distinguished from other hard clear minerals in the olden days?

Like quartz or other hard mineral vs diamond. How was someone in the olden days going to say “This is diamond not quartz” before the advent of of modern scientific analysis methods? How could they tell?

Having not even taken a geology class in my life, I could be wrong. But couldn’t they get a pretty good idea based on what could scratch what? If they had quartz and diamond the diamond would be able to scratch the quartz but not the other way around I would think. But I like I said, I really have no basis for saying that.

I don’t know about diamonds, but a lot of the “rubies” in those elaborate medieval crowns are actually spinels. The gems are also unfaceted.

I cannot find a cite for this, so please treat it a “could certainly be wrong” opinion, and not a statement of fact.

But somewhere or other, I recall reading that one thing they did was bash the stones with a hammer or rock. If it did not shatter, it was considered a diamond. The piece did mention that this could smash a diamond, too, and probably a lot of them were destroyed also.

Since I do not even remember what publication I read this in, I can’t even vouch for the integrity of said publication.

I did find it fascinating enough to remember, probably 30 years or more afterwards.

Maybe someone else can verify or put the kibosh on this tale?

An experienced jeweler can distinguish various gems by eye, based on their refractive and dispersive properties. I think that diamond has a higher index of refraction than anything else known to the ancients, so it would be particularly easy for diamonds.

Also, once Archimedes came along, it’d be fairly easy to measure densities, so long as it’s not set into some larger piece of jewelry, which would also pin it down.

Diamond in its pure form is colorless as well as hard and transparent. Pure macrocrystalline quartz has a very similar appearance.

There are many ways to tell the difference:

As Chronos already mentioned, pure diamond refracts light such that you can see a prism of colors; quartz does not. I suspect making this obsevation would be the easiest method of differentiating diamonds from other minerals.

Pure diamond scores a 10 on the Mohs scale of mineral hardness; quartz is a 7.

Specific gravity (i.e. density relative to water) of pure diamond is 3.52; specific gravity for pure quartz is 2.65.

Quartz has piezoelectric properties while pure diamond insulates electricity.

Remember, though, in “olden” days, gems weren’t faceted, which made it harder to see the differences in like-colored stones. Hardness would have been a more reliable guide, but here again it could lead to false results. For instance, a clear white sapphire would have been able to scratch anything other than a diamond, and in the absence of a diamond to test it against, would have been mistaken for one.

Since stones were often merely polished, in some cases the shape of the stone might indicate that of the crystal when mined. For instance, one of those spinels masquerading as “rubies” is the Black Prince’s Ruby; to a modern eye it clearly suggests the octohedral shape in which spinel crystallizes.

When I saw “The Nature of Diamonds” exhibit a few years ago (American Museum of Natural History), one of the many interesting things I learned is that loose diamond crystals actually are diamond-shaped, that is, shaped like the “diamond” on playing cards. The crystal is an octahedron, the shape of two pyramids joined base-to-base.

Besides the distinctive shape, they are extremely hard and nearly unbreakable (nearly, because diamonds sometimes shatter if hit along a cleavage plane; if you’re not a diamond cutter, hitting one just right is a matter of pure chance, or bad luck). So in this form, at least, they were readily recognizable even in ancient times. The Romans considered them good-luck charms because of their durability. They are a bit tricky to set in rings, though, being pointed on both ends and all corners in the middle.

You’re close. If it shattered and a woman screemed then it was a diamond.

How desireable were diamonds back then? Without Debeers, were diamonds even as highly desired as they are now?