I would like to know if there'd be any way to forge a metal with an amorphous natural glass such as opal or obsidian into an alloy. Could such a thing be crafted into tools? Would it be conchoidal cleavage or a ductile split?

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    $\begingroup$ If you're interested in real-world alloys, considered asking on a chemistry or physics SE site? $\endgroup$ – Xen2050 Nov 26 '17 at 8:30
  • $\begingroup$ related: xkcd.com/1114 $\endgroup$ – Raditz_35 Nov 26 '17 at 10:18
  • $\begingroup$ Cast iron. Electrical steel (aka silicon steel). $\endgroup$ – AlexP Nov 26 '17 at 11:50
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    $\begingroup$ I have voted to close this question as it is not about worldbuilding, but about chemistry in our real world. If you can explain why this is important in the world you are trying to build, it may allow the question to be reopened. $\endgroup$ – JBH Nov 26 '17 at 15:39
  • $\begingroup$ I'm trying to write a fantasy world, I plan to attribute certain powers to the glassy solids listed above and want to know if such an alloy could be used for making a sword that would carry the abilities $\endgroup$ – Chris F Nov 26 '17 at 16:28

It sounds like “pig iron”.

The inclusions of stuff that’s not metal makes it brittle and is considered poor. Great effort goes into getting rid of that stuff!

Note that obsidian is glass — mostly silica — formed by melting certain minerals in lava. The smelting pot pretty much does the same thing! So pig iron is exactly whay you are describing.


The properties of an alloy, mixture or compound depend on its constituents, the chemical and physical bonds formed between them and on the process used to create it. Because an alloy contains a metal that is hard, shiny, tough, brittle or ductile does not mean that its alloys will “inherit” these properties, although they might, depending on circumstances. Obsidian and opal have a variable composition although are made mostly of silicon dioxide, so it would probably be easier to use sand.

A lot would depend upon the process used to mix them. The original amorphous structure of the obsidian or opal would be totally destroyed by any extreme heat process and a new structure would be formed depending on the proportions, the presence or lack of other impurities, the temperature reached and the method of cooling among other things.

High silicon content iron alloys tend to show excellent corrosion resistance, however they also have low strength and impact toughness, high hardness and brittleness, poor welding ability, low thermal conductivity and high thermal expansion coefficients leading to casting defects and an inability to withstand thermal shocks. Iron – silicon alloys are often useful as magnets

As a side note the irradiance seen in opal is caused by the presence of 6-20% water trapped in the crystal structure. Extreme heating of opals will destroy this irradiance.

  • $\begingroup$ I don't think you could really get a metal/glass alloy, as alloys require mixing on the atomic scale. What you might get is some sort of a composite, like fiberglass or carbon fiber, with fine metal whiskers embedded in a glass matrix. Searching "metal glass composite" on Google returns about 12.5 million hits. $\endgroup$ – jamesqf Nov 26 '17 at 18:44
  • $\begingroup$ I supposed the OP is using “alloy” in a very loose metaphorical sense. Technically, his description is an oxymoron. $\endgroup$ – JDługosz Nov 27 '17 at 10:20

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