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[AxiumCog]

I think magma should cool into a random material. Either a type of igneous rock, metal ore, possibly even native metals. I think its more realistic than to know that when you cool it it will always turn into obsidian.

[NW_Kohaku]

I don't think it should be straight-up random.  Different types of igneous rock are specifically formed by the way in which they cooled (which is the difference between igneous intrusive and igneous extrusive, after all), but it would be nice if we somehow had a way to prospect that obsidian for some small chance of obtaining those metals that occur in volcanic deposits.  (Of course, that much can be done by modding.)

That said, however, I'm not expert enough that without going on a quick researching spree, I can say for sure what types of igneous rock can be necessarily formed by quick-cooling lava.

[G-Flex]

Ironically, obsidian forms specifically in anhydrous conditions; you'd never get it from mixing molten rock with water.

[AxiumCog]

Its my understanding that modding only changes what the magma will cool into. Its ether all obsidian, or all whatever you modded it to turn into.

I like the idea of the WAY you cool it affecting what it turns into, but i still think there should be some chance of metal ores etc to appear. After all, magma is molten rock, metal, carbon, everything. So even gems could theoretically be manufactured to some extent.

Obsidian is a type of glass if im not mistaken as well isnt it?

[G-Flex]

So even gems could theoretically be manufactured to some extent.

Gems are in no way special in terms of the substances they're made out of, though; they're just relatively clean crystals of what is usually common stuff. But yeah, volcanic activity is pretty good at creating them.

Obsidian is a type of glass if im not mistaken as well isnt it?

Yep, it's a form of volcanic glass.

[NW_Kohaku]

Its my understanding that modding only changes what the magma will cool into. Its ether all obsidian, or all whatever you modded it to turn into.

I like the idea of the WAY you cool it affecting what it turns into, but i still think there should be some chance of metal ores etc to appear. After all, magma is molten rock, metal, carbon, everything. So even gems could theoretically be manufactured to some extent.

Obsidian is a type of glass if im not mistaken as well isnt it?

Obsidian is a volcanic glass, but don't be confused by the term, "glass" is a far broader term than you might think.

Strictly speaking, a glass is defined as an inorganic product of fusion which has been cooled through its glass transition to the solid state without crystallising. ... The term "glass" is, however, often extended to all amorphous solids (and melts that easily form amorphous solids), including plastics, resins, or other silica-free amorphous solids.

To make it really, really simple, solid matter can be divided into "crystaline" (the atoms are in an orderly pattern), or "glass" (the atoms are in a disordered jumble).

What I was saying was that you could create a mod where you could smelt obsidian like you smelt ores like galena, and give yourself a small percentage chance of getting some of the metals that occur in volcanic layers, like copper or gold.  (In fact, some people already mod in extreme low chances of finding ore by smelting all their stone just as a way to dispose of large quantities of stone.)

I guess I'll do a little research, and get back to you on what sort of stones you should really be expecting to get out of water-cooling magma, though...

[NW_Kohaku]

OK, now remember that part about things being either crystal or glass?  Well, the way this works is, the slower magma cools, the more that the resulting stone is stratified and crystalized because the atoms have more time to re-arrange themselves into crystaline patterns that they prefer when the magma transforms from liquid to solid.  (Think in terms of water making ice - ice near the freezing point is less dense than regular water because it crystalizes into an orderly, and not terribly closely packed formation (due to the magnetic forces that water exerts.))

Obsidian is a glass because it is magma that cools so fast that it cannot form orderly patterns at all, and as such is just a dense, evenly (yet chaotically) mixed lump of random minerals, as opposed to, say, granite, where you can actually see the veins of different minerals.

I'm still trying to look up what are likely stones to be made from contact with water, but not at the great depths of mid-ocean ridges (which are apparently basalt and gabbro)

edit: oh, here's a few hydrated volcanic glass: http://en.wikipedia.org/wiki/Hyaloclastite http://en.wikipedia.org/wiki/Sideromelane http://en.wikipedia.org/wiki/Tachylite and http://en.wikipedia.org/wiki/Palagonite  Note: these are all considered to just be glass versions of basalt (that is, more quickly cooled basalt).

[G-Flex]

For what it's worth, hydrated obsidian tends to form perlite.

But yeah, NW_Kohaku's explanation is pretty much right. You can even get a form of glassy ice (amorphous ice) if you freeze it quickly enough, but this rarely ever happens naturally.

[NW_Kohaku]

But yeah, NW_Kohaku's explanation is pretty much right. You can even get a form of glassy ice (amorphous ice) if you freeze it quickly enough, but this rarely ever happens naturally.

Specifically,

The key to producing amorphous ice is the rate of cooling. The liquid water must be cooled to its glass transition temperature (about 136 K or −137 °C) in a matter of milliseconds to prevent the spontaneous nucleation of crystals.

So it only happens in nature if you consider the vacuum of space nature.

For what it's worth, hydrated obsidian tends to form perlite.

The difference between these, however, is in their chemical compositions.  The difference between the more common tachylite and the less common sideromelane is in the presence of iron (tachylite has iron), not the way it cools.  We could theoretically create a list of what essentially amounts to the same set of igneous rocks we have, and their hydrated glass form... although that would be perhaps on the needlessly complex side of things, especially considering as all the igneous extrusive rocks we have now are almost entirely functionally equivalent (really, the only major difference is that some are now magma safe, and others are not).

[NW_Kohaku]

I'll have to do more reading tommorow, but from what I'm getting from this, Basalt is just extrusive Gabbro, Andesite is extrusive Diorite, and Rhyolite is extrusive Granite.

The difference between the three pairs is in their mineral composition.  On one side, you have "Mafic" (a concatination of Magnesium and Ferric, which are unusually common in these stones, while sillicates (SiO₂) are unusually low), which are the basalt/gabbro pair. On the other side, you have "Felsic" (High sillicate composition), which is the Granite/Rhyolite combo.  Andesite/Diorite is in the middle between the two.  (There's also another category of "Ultramafic" rock, which forms a Komatiite/Peridotite pairing, although neither stone are currently in DF.  Kimberlite, however, is an ultramafic stone that is in the game... and that's the stone that you search for diamonds in.)

Wikipedia is talking about how this is intrinsic to the magma flows themselves, and talks about how things like Andesite (magma) is formed by mixing rhyolitic magma with the basaltic magma, which basically occur on the faultlines of tectonic plates, implying that you would not expect multiple types of magma to be available in any one location (so, you get one of those types of magmas, and that's it), although I'll have to do further reading.


If we have areas that are specifically one kind of magma, with that specific kind of igneous rock, we could specify exactly what non-hydrated and hydrated glasses they should form.  If it is map-wide, it would only have to be a single variable for the entire map, making it fairly resource-light.  Since these different stratifications have different chemical compositions, we could basically make this good for handling the probabilities of different ore deposits, so that iron ores are more common in mafic stones.

There is, however, a problem.  Most of these hydrated glasses that are formed are, essentially, pumice-like stones.  That is, they are ultra-light, and not useful for direct application as stone, although they can be ground up into a soil, or used as plaster.

I'm thinking it might be possible, however, that "hydrous" doesn't mean what I first thought it meant, based on what G-Flex said.  Hydrous magma seems to just mean that there is water in the magma (before it cools), rather than that it cooled specifically because of contact with water.  The hydrous glass is light and pumice-like because the water in it manages to escape the stone as water vapor as the magma solidifies...  This is complicated because there doesn't seem to be a specific wikipedia page on the subject matter...  I'll just do a broader google search tommorow.

[Xenoc]

Not a bad go at the felsic/intermediate/felsic system at all 

Generally you will find only one of those basic pairs at a single volcano - the magma chamber and derived dykes and sills will dontain the intrusive version, the eruptive products will comprise the extrusive (i.e. faster cooled, therefore finer grained) versions.

However, ALL magmas are originally mafic in composition.  It is the process of cooling as the magma rises through the crust which causes variation.  Minerals with high melting points will crystallis out first, leading to a process known as fractional crystallisation.  Because the early-crystallising minerals are generally rich in iron and magnesium, and low in silica, as they are removed the remaining melt is relatively enriched in silica and depleted in iron and megnesium. 

Now imagine a magma chamber under a volcano:  It is periodically recharged with pulses of mafic material from the mantle, but a constant process of fractional crystallisation is going on.  If an eruption taps that magma chamber at intervals, then the type of magma erupted will depend on where in the fractionation cycle the magma chamber is at that point, leading to a variety of magma compositions being possible at any given vent.

This can be further complicated by volcanoes which have multiple active magma chambers, each of which may be tapped individually or in combination, often with their own volumes, cooling rates, and recharge periods.  It can get very complex very quickly.  However, broadly speaking volcanoes sit within one of the three broad magma groups stated above (in actual fact there are numerous subdivisions and classifications within those three broad groups).

The simplest way to think about volcanoes is those which have a mafic, mantle derived source produce runny lava and form broad low-angle slopes, such as those on Hawaii, while the opposite end of the spectrum has the highly evolved, silica rich magmas. These are very viscous and unable to move effectively as lava, so tend to form large explosive eruptions such as Mt St Helens and Pinatubo.  These volcanoes are steep sloped (about 30 degrees).   

On the subject of obsidian formation - you tend to see this produced mainly in rhyolite (i.e. felsic) eruptions - usually localised as spires or domes of material are extruded from the vent over a period of months or years.  Mixing magma and water should only really produce a very deadly pyroclastic cloud, full of steam, ash and death. 

[G-Flex]

I'm thinking it might be possible, however, that "hydrous" doesn't mean what I first thought it meant, based on what G-Flex said.  Hydrous magma seems to just mean that there is water in the magma (before it cools), rather than that it cooled specifically because of contact with water.  The hydrous glass is light and pumice-like because the water in it manages to escape the stone as water vapor as the magma solidifies...  This is complicated because there doesn't seem to be a specific wikipedia page on the subject matter...  I'll just do a broader google search tommorow.

I don't think that's the case. From the Wikipedia article for "Obsidian":

Obsidian has low water content when fresh, typically less than 1% water by weight,[4]  but becomes progressively hydrated when exposed to groundwater, forming perlite.

[Footkerchief]

Not a bad go at the felsic/intermediate/felsic system at all 

Generally you will find only one of those basic pairs at a single volcano - the magma chamber and derived dykes and sills will dontain the intrusive version, the eruptive products will comprise the extrusive (i.e. faster cooled, therefore finer grained) versions.

However, ALL magmas are originally mafic in composition.  It is the process of cooling as the magma rises through the crust which causes variation.  Minerals with high melting points will crystallis out first, leading to a process known as fractional crystallisation.  Because the early-crystallising minerals are generally rich in iron and magnesium, and low in silica, as they are removed the remaining melt is relatively enriched in silica and depleted in iron and megnesium. 

Now imagine a magma chamber under a volcano:  It is periodically recharged with pulses of mafic material from the mantle, but a constant process of fractional crystallisation is going on.  If an eruption taps that magma chamber at intervals, then the type of magma erupted will depend on where in the fractionation cycle the magma chamber is at that point, leading to a variety of magma compositions being possible at any given vent.

This can be further complicated by volcanoes which have multiple active magma chambers, each of which may be tapped individually or in combination, often with their own volumes, cooling rates, and recharge periods.  It can get very complex very quickly.  However, broadly speaking volcanoes sit within one of the three broad magma groups stated above (in actual fact there are numerous subdivisions and classifications within those three broad groups).

The simplest way to think about volcanoes is those which have a mafic, mantle derived source produce runny lava and form broad low-angle slopes, such as those on Hawaii, while the opposite end of the spectrum has the highly evolved, silica rich magmas. These are very viscous and unable to move effectively as lava, so tend to form large explosive eruptions such as Mt St Helens and Pinatubo.  These volcanoes are steep sloped (about 30 degrees).   

On the subject of obsidian formation - you tend to see this produced mainly in rhyolite (i.e. felsic) eruptions - usually localised as spires or domes of material are extruded from the vent over a period of months or years.  Mixing magma and water should only really produce a very deadly pyroclastic cloud, full of steam, ash and death. 

That's extremely educational, thanks!  I'm 100% in favor of deadly pyroclastic clouds.

[cephalo]

That's extremely educational, thanks!  I'm 100% in favor of deadly pyroclastic clouds.

It used to be that way! I remember steam traps from 2D.

[Deteramot]

So it only happens in nature if you consider the vacuum of space nature.

I'd just like to point out, because I'm a nitpicker like this, that, while space is exceedingly cold, vacuums are very good insulators. As there isn't a lot of matter for heat to transfer to, things in space cool very slowly, which is why realistic stealth devices would never exist in real life, because the spaceship would be hot from it's engines firing and life support and would be incapable of bleeding that heat into it's surroundings.

Glassy Ice would be formed by dropping a glass of water into something like liquid nitrogen.

Anyway, I do agree with the OP. It would be nice for magma flows to cool into other types of stone.