I’ve been coming across videos of people breaking obsidian chunks to make arrowheads but could never find the answer why it could be broken with light hits with a rock, and then not break when in use with said weapon.
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Because it’s incredibly sharp.
It’s used in arrowheads because you don’t need to worry about them breaking; you need em to penetrate.
It’s used in daggers because it holds an edge for a long time; good for piercing and slicing.
Obsidian isn’t used in many large weapons because of how brittle it is. Obsidian “swords” are just clubs with easily-detached obsidian razors along the side.
In most cultures where obsidian tools were common, obsidian was also the only naturally occurring blade material side from stone (without metal, that makes it very useful)
Used? Was used.
Reason: Very sharp and relatively easy access where it can be found, easy to work with, also pretty.
Also, the assumption that it is not broken when used in weapon is wrong. It gets broken, constantly. Except that people brake obsidian to get a usable shape to use as a weapon. An obsidian edge will always be crazy sharp. This means that once made into a weapon, it doesn’t matter if it breaks anymore, the general shape is conserved, and this can even be said to be self-sharpening. You may strike, it may be blocked, but the impact will break off a flake of the blade, resulting in a sharp edge again, while a flint edge would have just blunted.
Obisidian arrowheads and other tools are essentially stone age technology. The tech is no different from flint arrowheads and knifeblades, something done in a culture before metal becomes available and common. Copper and bronze are rare and expensive even now, so any place that is yet to discover or get good ways of refining iron on a larger scale is stuck with stone like obisidian for some of its consumable items.
Commenting on ELI5 Why is obsidian used for so many weapons even though it is very fragile?…
Razors are also extremely fragile but extremely sharp at the same time. If you make a very sharp arrow or spear point you only need it to be effective once. If you recover the point you can easily sharpen it again with the same methods as the original construction. If that was a modern razor sharp arrow tip you would need to replace the tip instead of just perfecting the edge, so it’s arguably better if you want to hunt regularly.
Relatively plentiful in areas where you can find it, pretty easy to shape, you can use the really sharp pieces formed from making other tools to make small things like arrowheads and knives and most importantly it can become one of the sharpest objects in history. Under a microscope I’ve been told that if you cut an individual cell with an obsidian scalpel you get a clean cut if you cut it with a metal implement it looks like a chainsaw ripped it apart
Regarding your concerns about breaking it, search an image of Macuahuitl, it was an ancient Aztec weapon that had individual obsidian blades, this weapon was brutal and effective. Also, the arrangement of the obsidian teeth allowed for them to be substituted individually if needed.
Because it can be extremely sharp.
When it comes to arrowheads, it doesn’t matter if the obsidian breaks once it’s hit the target. If anything, it may result in further injury to the target.
For reusable tools, reshaping the obsidian edge or replacing it if it’s beyond use would have been a fairly easy task for a skilled craftsman. Spending a few hours creating a new knife blade was time well spent if it meant dressing a deer. And as I understand it, an obsidian knife used for skinning could last a very long time.
As long as the tool is used for its purpose, it should be fine.
Since obsidian will fracture down to a single atom, it is claimed to have a cutting edge five hundred times sharper than the sharpest steel blade, and under a high magnification microscope an obsidian blade still appears smooth, whereas a steel blade has a saw like edge
All tool materials are a compromise. And the native Americans at least had no steel or bronze technology. So they used what they had, glass. Glasses including obsidian are actually fairly hard, and they are easy to fracture into a shape with an extremely sharp edge, much sharper than you could ever get steel. In fact a fresh obsidian edge can be hard to see even under an electron microscope. Glass breaks along lines of atoms .
But really the answer is obsidian was all they had. I guess bone was an option and fire hardened wood and other rocks similar to obsidian
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