Could be a little challenge to find functions giving certain types of stones in great variability. Also, there might be some definition needed for it, to make the engine know, where what type of rock should be (in terms of local layers) and some blending between them. You would probably need some 3D map of mineral layering (but maybe some simple function with height and biome-type surrounding could be used too) for the whole globe - not sure if something like that was ewer done in scientific terms even in rough data-displacement. It would be really classy to have that, as ores and special minerals could be defined and modified for each planet (and greater realism achieved), but that would need probably some terrain modification tools too, to check, if ya can dig to that place to find, if its right, where it should be ... (and for us to speculate with - that means caves to be implemented too). ... and i need to make a heavy-tractor for that. ![Cheesy :D](http://forum.outerra.com/Smileys/default/cheesy.gif)
I'm not that savvy on technical things (and many other things haha), so this might be a naive idea, but wouldn't it be possible to label certain rock types directly into the source data for the world making? Maybe a second, hand-crafted, data source or something akin to how biomes work? Or even one map for elevation, another one just for the rock type?
(Again, really ignorant me trying to get the idea through)
http://i.imgur.com/idg2DzY.pngWhere:
-Red is Limestone (
http://seekraz.files.wordpress.com/2010/08/limestone-mountain.jpg)
-Sky blue is Hawaiite (
http://people.whitman.edu/~pogue/images/climbing/royal.jpg) and
-Yellow is Adakite (
http://plate-tectonic.narod.ru/volal-adak_tundra.jpg)
Wouldn't make sense in this case, it's just an example.
The outcome wouldn't be absolutely realistic, but it would add a lot of diversity and make the scenes more believable.
There could even be different fractals patterns for each rock type to get distinctive shapes. The same could be applied to coast lines so not all of them are just sand (or the same kind of sand, in Alaska and many other places, the coast is form by small spherical rocks).
There is more to it, mountains aren't shape sorely based on the type of rock (if anything, that's holds more relevance on the colouration and texture), the kind of erosion that affects the area would also close the gap between the real world and Outerra. But that does start to complicate things a bit too much. Maybe just setting up a couple of archetypes that would determinate the way rocks and elevations are made would give enough control to allow crafting believable landscapes.
Again, simple example:
-Sedimentary rock 1 (
http://www.earth.ox.ac.uk/~oesis/field/medium/quartzite.jpg)
-Sedimentary rock 2 (
http://anotherwalkinthepark.files.wordpress.com/2013/09/capitolreef_canyonlands1-3172.jpg)
-Igneous rock 1 (
http://upload.wikimedia.org/wikipedia/commons/d/d3/Ascension_Island_Black_igneous_rocks.jpg)
-Igneous rock 2 (
http://upload.wikimedia.org/wikipedia/commons/a/a5/S-Basalt.JPG) Polygonal basalt is awesome!
-Metamorphic rock 1 (
http://vagrantviking.com/images/Def%20and%20Met1.jpg)
-Metamorphic rock 2 (
http://saturniancosmology.org/files/geology/Sect2_1a_files/Slide1.jpg)
*Note: the metamorphic rock is, basically, some other type of stone modified by the action of some external factor (water, wind, etc), not something that would cover big landmasses, but would work perfectly for certain parts.
This would increase vastly the possibilities for fictional worlds, where people isn't expecting a 1:1 reproduction of how things look IRL and the creators can take some creative freedom.