How do I decide what resources are where?

[Adversary]

waldronate, You are not stomping on me. This is a complex subject and more views are welcome. The area I am in (west central Georgia) is quite different from your neck of the woods. The geologic processes are quite different but produce similar results. I live on the fall line that runs across central Georgia roughly east-west. South of us is "new" land made up of the coastal plains. It is sediment formed by the erosion of the ancient Appalachian mountains. It is good farm land as well as a good source of clays. Moving north of the fall line is the piedmont. The basement rocks are exposed revealing sedimentary and igneous gneiss. There is some mineral and crystal mining in this area and some farming but the topsoil is thinner. There is also coal in this area (of course it is on above the gneiss) and pine forests. The Appalachian mountains have been the source of gold mines, marble quarries, and some gem stone production. There are also copper mines. In the north west corner of Georgia is the valley and ridge provence. It runs up the western side of the mountains and consists of deep valleys and steep ridges running north-south. These are the eroded remnants of the folded land behind the Appalachian orogeny (mountain building event). This region is most notable in restricting east-west travel while generally making north-south travel easier by river.

The point of this rambling is this. Certain minerals, metals, gems or whatever, need a specific environment in which to form. But the transportation mechanism of these resources may play a more important role in where they are found. For example, gold is most often discovered in rivers first, but that is obviously not where it formed. Other resources, like marble, must by found where they formed. Once marble erodes it is no longer marble. Water is the most important transportation vehicle. liquid water can carry solid or dissolved materials great distances. Once the water slows or evaporates it can drop it's load. With a hydrothermal vent, super heated water can carry a variety of minerals from deep in the earth and deposit them on the surface by deposition. Frozen water in the form of glaciers can move vast amounts of material long distances. For example of diamonds from Canada being found in Wisconsin. They also scour the surface and can expose hidden veins of minerals that may have otherwise gone unnoticed.

[Gidde]

I think this thread has enough useful info (keep it coming, you two!) to move it to the How To/Tutorial section. Any objections before I do so?

[ltan]

Gidde, if not there then perhaps in the reference section!

[Gidde]

I was actually hemming and hawing between How-To and Reference, and you decided me, Itan. This thread now lives in the "Reference Material" forum.

[Adversary]

Coal is a valuable source of heat energy and for the purposes of this thread (which is turning into a bit of a rope) will be divided into five classifications. I will divide coal in order of quality or maturity.

Peat is the most basic form. While it is not technically coal, it is where coal comes from. Peat is a mixture of plant material (most commonly Sphagnum moss) that has died and become compressed in a wet, low oxygen environment. It is not quite a swamp but it is a wetland or mire in a cooler or moderate environment. Organic material decomposes faster in a warmer environment so peat may not have a chance to form. That said, peat can form in virtually any climate. The lack of oxygen keeps the organic matter from totally decomposing. Once the mire has aged a peat bog will be the result. It can take over a thousand years for a layer of peat about a meter thick to form. Peat can be dug up and cut into bricks which are dried. Peat can be burned for heat much more efficiently than wood or charcoal for home heating and cooking. Peat has also been distilled to produce naphtha. Other uses include fertilizer, bedding for cattle, filters for water purification, and to dry barley for some Scotch Whiskey distilleries.

Lignite coal is the next step after peat. Lignite coal has a brownish color and produces a lower heat than more mature coals. It is basically compressed peat that has become slightly carbonized under heat and pressure. It takes a few million years of heat and pressure to transform peat into lignite. This coal is the most abundant form of coal but it tends to give off more smoke and sulfur than more mature coals.

Sub-bituminous Coal is the first stage of "black" coal though it may still have the brownish color of lignite. It is more carbonized with about 42-50% carbon. This coal produces less smoke and sulfur than lignite but is still a soft coal. About half the worlds coal reserves are lignite and sub-bituminous coals.

Bituminous Coal is the most desirable coal in use today. It has a lower sulfur content, is plentiful and produces more heat. It is 60-80% carbon.

Anthracite is the highest grade coal. It has a shiny black appearance and is harder than the other types of coal. It has a carbon content of 92-98%. It is the cleanest burning of the coals and the hottest. During the American Civil War, the confederate steam blockade runners would burn anthracite because there would be little smoke from their stacks to give them away. Anthracite coal is also sometimes known as Blacksmith Coal because... well... it is good for blacksmiths. Oddly enough it is not the most popular form of coal because it burns too hot for most applications and it is the most expensive form of coal. Anthracite is also hard to ignite, but burns a long time once it is lit. It is most commonly used for home heating today.

Overall, coal is easy to find. It is found in most countries where sedimentary rocks are found. It will never be found with or below a granite layer. While thin beds are found most everywhere, thick commercial beds are somewhat less common. Some of the first deep mines were used to mine for coal. But it can be mined from exposures or strip mined if it near the surface.

This is a photo of bituminous coal in norther Georgia. The bottom layer is shale, then a thin layer of coal with sandstone on top.
CoalSeam.JPG

This is a modern deep mine in central Illinois. The conveyor covered belts carry most of the coal many miles directly to a power plant.
Coalmine.JPG

[Gidde]

Ok, so I've been reading these right along, but I want to make sure I understand correctly. The reason coal & granite never are found together is because coal takes a long time to form and the magma that makes granite would ruin it? I guess i'm wondering what would happen if a coal seam in process of formation rolled over a hotspot.

Granite has always confused me. I thought it was igneous, then I read it was metamorphic instead ... your post above says it's made from magma moving. I'm still very fuzzy. Can you pretty please talk about granite itself in a little more detail?

[waldronate]

Granite forms from sow cooling of a melted rock, which will almost always burn off any coal that's already there when the magma intrudes. Coal deposits from water (usually) buried under things, which is decided a non-melted environment. Note that very rare circumstances can results in coal touching granite, but it would require the presence of an unconformity (that is, the granite would need to be exposed and have coal deposited on top of it).

Granite is indeed an igneous rock; it's what happens as the melt cools slowly to form largish crystals. If the crystalized granite undergoes metamorphic processes, it forms a rock known as gneiss. The fun thing about granite is that its basic constituents (quartz, feldspar, and the other darkish crap left over from the other two) can be polluted in lots of ways to get pretty colors. Red granite, for example, is what happens with a little iron contamination in the feldspar. The about and size of the darkish grains broadly determines its overall darkness.

Granite is an intrusive kind of rock. It forms deep underground where a melt intrudes into an existing body of rock. The granite slowly cools, allowing the crystals to grow moderately large. As the quartz and feldspars crystallize, they force out lots of water and other materials. This hydrothermal (hot water) fluid forces its way out into surrounding rock, further metamorphosing it and depositing a lot of the stuff forced out of the cooling granite block. The heat itself will also distill off volatile fractions of the host rock, including organic materials such as coal. It can also cook off and mobilize relatively volatile rocks such as limestone and gypsum. Limestone gets cooked to marble if it can't get away.

The same material that forms granite can erupt on the surface where it usually forms a rock known as Andesite, a fine-grained and hard grayish rock.

[Gidde]

Thanks waldronate! That really helped

[Falconius]

Speaking of coal, it can also catch on fire leading to huge, remarkably hazardous and toxic, underground fires which burn for years. And they are actually fairly common. There is one in Alberta that they estimate has been going on for well over a hundred years. I may be mistaken but I thought natural gas also caused immense fires underground.

[Gidde]

Huh. You'd think those underground fires would quickly suffocate.