Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Dorf and Dumb]

You take some magma.  Mix with a little water and it stays liquid.  Mix with enough and it solidifies to obsidian.  So obsidian is just magma that's gotten a lot colder than magma.  So when you build something out of obsidian, why is it magma safe?

[MonkeyHead]

Latent heat. Presumably the same reason as how one could carve a chunk of ice into a cup shape and store water in it without the cup melting.

[Bki]

Because Obsidian's melting point is higher than the temperature of lava/magma? It may seems strange that the melting point of quickly-cooled-off lava/magma is higher than the temperature of magma. It is less strange when you consider the difference in pressure between deep in the earth were magma form and the surfaces/how deep your fort actually is (at the very least, this is what I remember from my half-forgotten understanding of geology and of the formation of magma. Someone more qualified may be able to give a more complete and correct answer).

Of course, we don't see lava cooling off when exposed to air like it should do. But I'm sure this is a problem that will eventually be fixed in a future release.

Also, water + magma doesn't give obsidian because the two "mix", but because water cool off the magma and thus form obsidian.

[Orange Wizard]

The raws for obsidian have the melting point set higher than the temperature of magma. There is a note there saying that it should be lower, but has been left (and will remain) higher until environmental magma effects "get further along", presumably things like magma cooling down in air + water.

[Edmus]

Could just be the structure of the crystal. like the whole diamond, charcoal graphite thing.

[Girlinhat]

Could just be the structure of the crystal. like the whole diamond, charcoal graphite thing.

That's pretty much it.  The molten rock is shocked cold, not just left to cool but made to very quickly cool, which changes the chemical composition slightly.  It's the same idea as having steel in the forge then left to cool, and having steel in the forge that's quenched cool - both are iron + carbon, but the process changes things.

[klefenz]

In the case of quenched steel there is no "slight" chemical change. No chemical change at all, atoms are not going anywhere. There is a distortion of the crystalline structure going from austenite to martensite. But this does not affect melting, because at such high temeperatures martensite transforms again.

I dont know that much about obsidian, but it forms from high silica magma (not just any magma) when quickly cooled impeding crystal growth. This lack of crystal growth turns it into glass (very small crystals and distorted crystalline structure). Again this shouldnt affect melting point, it should remain the same as the magma it came from.

The latent heat (glass of ice with liquid water inside) only work if they are sitting at the melting point. It could be the case in DF, since the temperature of magma is fixed, and its composition is not taken into account.

[Quietust]

The raws for obsidian have the melting point set higher than the temperature of magma. There is a note there saying that it should be lower, but has been left (and will remain) higher until environmental magma effects "get further along", presumably things like magma cooling down in air + water.

This is the correct answer - obsidian is supposed to have a melting point of 11818 (which is not magma-safe), but Toady changed it to 13600 (which is magma-safe) because otherwise certain things wouldn't make sense (such as magma being surrounded by non-magma-safe obsidian).

[Kamamura]

You overcomplicate stuff. Obsidian is magma safe in minecraft too, and that's enough of a scientific proof for me.

[ArmokGoB]

You overcomplicate stuff. Obsidian is magma safe in minecraft too, and that's enough of a scientific proof for me.

Literally everything is magma-safe in Minecraft.

[Torrenal]

Trees and wood in minecraft are not magmasafe.

You're missing out if you haven't dropped a bucket of magma on top of a tree...

but I digress...
In DF, the simple thing is magma needs magma safe rock to hold it, or else magma may melt the entire map, dropping everything, elves, goblins, and dwarves into Armok's blood.  The presence of obsidian is easy to explain "The obsidian is lava that cooled on contact with the rock..."
If not obsidian, it'd need to be something else.  The presence of candy-lined magma tubes, while very exciting, would also generate far more debate.  Who put the candy there?  Does the candy grow out of magma?  Or does the magma grow out of candy?

I've not forgotten the humans.  They've been crossbreeding with the owl-people, and have thus obtained flight.
//Torrenal

[Orange Wizard]

Trees and wood in minecraft are not magmasafe.

They're not fire safe. If you stop them from catching fire, lava can do nothing to them.

[Fat Friar]

If not obsidian, it'd need to be something else.  The presence of candy-lined magma tubes, while very exciting, would also generate far more debate.  Who put the candy there?  Does the candy grow out of magma?  Or does the magma grow out of candy?

//Torrenal

I really like that last idea, that the rarest substance known to dwarfdom somehow secrets the most valuable substance known to dwarfdom.
I'm imagining a miner staggering home every day conflicted, brooding over a microcline mug of booze, driven to the edge of insanity by his moral conundrum. How deeply can we mine the bones of Armok, before the blood of Armok runs dry?

[Saiko Kila]

I know it's not modelled in DF, but in real life obsidian is a glass, and forms through glass transition, which happens without phase change. In other words obsidian is still a liquid, it just doesn't know it yet. In glass transition there's no "freezing" temperature. Nor there is a "melting" temperature when you heat up a glass piece, it is just becoming less and less solid and more and more runny.

Funny thing about real life glass is that "melting" (complete softening) of it is usually at a higher point than the "freezing" (glass transition when producing glass). Also, the temperature of "melting" depends on manner of previous "freezing", mainly how fast was that "freezing" performed, and the bigger differences are observed when cooling rate is much different than heating rate. Which means it is possible to have item not melt in the magma they are made from. Though they should be more soft and elastic than the rigid obsidian at room temperature, so obsidian pumps should probably stop working efficiently and even jam.

Personally I doubt that glass formation and melting will be modelled accurately in the DF, because it adds nothing to the fun I believe, and is not needed. Similar effects can be achieved by currently used approximation and some in-game cheating (like using a fixed "melting" point, even if there's no such thing in real glasses). But who knows.

[greycat]

the rarest substance known to dwarfdom

Common sense?