After eating my Khorne Flakes, from a sudden idea and playing too much Minecraft, I wanted to make a monomolecular obsidian edged weapon (not just throwing knives and arrowheads).


What's the most convenient way of achieving this, and I don't want to carry dozens of swords to the battlefield as "replacements".

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    $\begingroup$ Against leather just do what the Aztecs did. A club with small obsidian blades. Those could supposedly cut of limbs through cloth and leather armor. $\endgroup$
    – Mormacil
    Mar 18, 2017 at 21:37
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    $\begingroup$ You do know that obsidian is nothing more than regular fused silica glass, but made in very unclean conditions and with wildly uncontrolled composition. It has all the bad properties of glass and few if any redeeming qualities. It's not even cheap. $\endgroup$
    – AlexP
    Mar 19, 2017 at 0:15
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    $\begingroup$ "Normal" glass, as in cheap window glass, is soda-lime glass, made of silica (about 70%), sodium oxide and calcium oxide. Obsidian is made of silica (about 70 to 75%) plus whatever was there in the molten lava, usually magnesium oxide and iron oxide. Both are quite hard and very brittle and when broken present very sharp edges (as in monoatomic-sharp). Neither is useful as a weapon unless nothing better is available, for example because you are an Aztec living in the stone age... $\endgroup$
    – AlexP
    Mar 19, 2017 at 0:31
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    $\begingroup$ @RedactedRedacted: Obsidian, just like ordinary glass, is very brittle. It will shatter in many pieces when hitting any reasonable shield or armor. Sharpness isn't everything, you want your weapon to remain in one piece. The advantage of an (relatively dull) iron sword over a (sharp) bronze sword is that the iron sword will survive in one piece and can be beaten into shape, re-sharpened and re-used after the battle... $\endgroup$
    – AlexP
    Mar 19, 2017 at 0:40
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    $\begingroup$ A bomb with deadly sharp obsidian shrapnel can be deadly. $\endgroup$ Mar 19, 2017 at 4:53

5 Answers 5


I don't understand why you need nano to make things out of obsidian. Make your cutting edge out of obsidian. If you have a metal cutting edge you sharpen it when it gets dull. If your edge is a fracture plane (as with obsidian) then when your edge gets dull you make a new fracture plane with a sharp edge.

Your cutting implement will be smaller in proportion to how much you fracture off (glass) or file away (metal). Ideally not too much. Does nano help with making tiny fracture planes? If so, great - bring your nano with to the battlefield. I am sure people with metal blades brought sharpening stones.


Replaceable cutting edges. These things are going to break, so you'd need a lot. But along the lines of razor blades, all you need is the cutting edge, so have weapons designed to just fit a new edge. Best to have multiple replacements within the weapon itself.

Like a mechanical pencil, press a button and a bit more edge extrudes itself. Press another button and the edge retracts into the weapon.

In fact this could be a very nasty weapon if it could also fire the edges. Imagine a thrust into the torso or even arm or leg, press a button and edges are expelled into the body causing all sorts of grief. It's a weapon with multiple possible uses. If fighting armour retract edge and bludgeon, if no armour, extrude edge, if you score a thrust, expel the edges in the body. If you force it into a chink in the armour, expel the edges inside the armour.

  • $\begingroup$ Actually, and older form of tool for material cutting for electron microscopy was made from brittle glass fragments. More or less you break your glass to get a knife for each use. $\endgroup$ Jul 25, 2018 at 12:27
  • $\begingroup$ @OlegLobachev glass can be knapped like flint, you pressure flake it. $\endgroup$
    – Kilisi
    Jul 26, 2018 at 0:30

Natural obsidian is a pretty terrible substance to make a durable weapon with, but there are other "obsidian like" materials that could work. "Obsidian like" being glass with impurities...

Consider: http://www.popsci.com/technology/article/2011-01/new-metallic-glass-toughest-strongest-material-yet

The glass, a microalloy made of palladium, has a chemical structure that counteracts the inherent brittleness of glass but maintains its strength. It's not very dense and it is more lightweight than steel, with comparable heft to an aluminum or titanium alloy. "It has probably the best combination of strength and toughness that has ever been achieved," said Robert O. Ritchie, a materials scientist at Lawrence Berkeley National Laboratory who is one of the authors of a paper describing the new glass. "It's not the strongest material ever made, but it's certainly one of the best with a combination of strength and toughness."

This material seems like it would work well, fairly light weight, strong, and tough.


Obsidian breaks because it is extremely rigid. You need Flexi-Obsidian, add a little springiness and you should have a more durable weapon.

When the weapon experiences a severe shock and starts to shatter, the nanites along the fracture point react by kicking out enough heat to re-melt the glass a little bit. Once it cools, the weapon is back in business.

Better make sure the first swing counts.

Extended duels won’t go well for this blade. But I could see a team of people in a combat situation, where the person with the obsidian blade makes one mighty chop and then ducks behind some teammates for a second while the blade cools down. Or maybe it’s only used when it’s snowing.

I don’t believe this is a practical blade, but if you MUST have obsidian, this solution might be somewhat believable.

  • $\begingroup$ heat flows too slowly compared to how fast fractures form. even if the nannites were ably to instanly become thousands of degrees they will not be able to stop the fracture. $\endgroup$
    – John
    Jun 6, 2020 at 15:16

You put a science-fiction tag on the question, so that opens the door on a rich history of great works and greater writers from whom we can borrow ideas.

Stasis - Larry Niven suggested the idea of a Stasis Field, within which the passage of time and all subatomic motion ceases. The arrangement and energies of the particles within a stasis field cannot be changed or rearranged while the field is in effect. If the blade of your obsidian sword is permanently sealed within a statis field, it will remain sharp and unshattered through the end of time. From there, you simply need to find a method of swinging it with adequate force to cut through armor...

Which much to wolverine's embarrassment, is a lot more force than any human arm can provide.

  • $\begingroup$ Well, if you're going to use a stasis field, you might as well ditch the obsidian and use only a stasis field. If stasis fields "have a perfectly reflective, shiny surface nearly invulnerable to outside damage", then what's inside will be mostly irrelevant. $\endgroup$
    – Jason C
    Mar 19, 2017 at 15:01
  • $\begingroup$ @JasonC, Agreed! But the OP specifically wanted monomolecular obsidian. $\endgroup$ Mar 19, 2017 at 16:34

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