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[Mel_Vixen]

Guys? Back to magma please or this thread gets closed by toady because it derailed to much (even if i like the current stealthing discussion.)

Ok how would different variants of magma affect worldgen? Like are there any moddels which simulate how a volcano grows based on the magmas materials? I could imagine that a volcano with high metal contents in the magma grows slightly different in comparsion to a volcano with low metal contents.

[NW_Kohaku]

Ok how would different variants of magma affect worldgen? Like are there any moddels which simulate how a volcano grows based on the magmas materials? I could imagine that a volcano with high metal contents in the magma grows slightly different in comparsion to a volcano with low metal contents.

Like has been said earlier, different magmas create different stones when they cool.  You get granite instead of a gabbro if the magma has become felsic by bleeding off its iron and magnesium ores to cooling lower down.

According to what I've read, and what Xenoc said, while it isn't something particular to mafic magma itself, mafic magma tends to be the runny-flowy type of volcano with low slopes, thanks to the fact that it's the magma that pretty much just bubbles up straight from the core of the Earth to a hole in the Earth's crust, and just sort of bubbles and spews and flows, such as the volcanos at the bottom of undersea trenches, in Iceland, or in Hawaii.

Felsic magma is magma that has had time to cool off a little, and has been compressed in an isolated magma chamber below the earth (where the magma has time to sort itself out, and the iron can solidify into ores, making the magma felsic in the first place), and as such tends to be found in your Mt. St. Helens or Varsuvius variety of pyroclastic volcanos that blow off the top of the whole mountain when the pressures finally get too great.  They also have the steeper slopes, and tend to make "lava domes" (pushing the land upward) as pressure builds.

[Xenoc]

To clarify a point or two there:

When a magma is crystallising in a magma chamber the ferromagnasian minerals which crystalise do not form an ore as such.  The minerals formed are things such as augite, pyroxene, and calcium-rich feldspar.  These silicate minerals are difficult to break down and not enriched enough in those metallic elements to warrant processing for metal.  It would be like calling basalt an ore rock.

Secondly, lava domes are not pushed-up land - these things are like very very sticky lava flows.  The lave is onthe surface, but extruded very very slowly indeed.  There's a big one developing inthe Mt St Helens crater at the moment:


Finally, sorry about the confusion on the obsidian thing.  The fact is that most geologists in the field will describe a volcanic glass as obsidian.   You can only distinguish a fresh tachylite from obsidian by expensive chemical analysis, so obsidian acts as a catch-all term a lot of the time.  In the same way, people describe mafic lavas as basalt, when actually they should really be calling them basaltic.  The fact is that basalt is a chemical term which can only be defined through analysis, and many geological maps describe things as basalts which are actually basanites or phonolites etc etc.