Rocks, Minerals, and Ores. A (Long) Introduction.
3 Big Rock Types
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation.
Igneous rock is formed through the cooling and solidification of magma or lava.
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. (Yeah they are the most complex).Metamorphic rocks are formed when existing rock is transformed physically or chemically at elevated temperature, without actually melting to any great degree.
Where do you find these rock types?
Sedimentary:
Basins, Top layers of Platforms,
Igneous:
Large Igneous Province, Shields, Orogens, Plate boundaries,
can be found as intrusive rocks elsewhere, but this implies things about the geologic history.
Metamorphic:
Orogens, Shields, Plate Boundaries, Platforms below the sedimentary layers
Igneous
Sedimentary Rocks
Sedimentary rocks
Common in occurrence, found in at least some amounts almost everywhere, but rare by volume. Usually exists as a thin layer ("strata") on top of other types of rocks.
Composed of either geological detritus originating from erozion of other rocks, or biological detritus originating from the accumulation of organic matter. As such, the chemical composition of a sedimentary rock depends on how and from what it has formed.
Clastic Sedimentary rock
Composed mainly of geologic detritus in the form of rock fragments of various sizes. Subtypes of clastic sedimentary rock are categorized by the size of the fragments that compose it.
Conglomerate Rock & Breccia
Composed of gravel sized fragments. Often found in riverbeds, beaches, on the slopes of eroding mountains, or near glaciers.
Economically, Conglomerate rock are generally most useful as a source of gravel, but in the case where the eroded material that has formed the conglomerate rock is valuable, the conglomerate rock itself may be considered valuable as well, but even then the rock may be most useful as an indicator of a nearby ore or precious stone deposit.
Sandstone
Composed of mainly sand sized fragments. Most often composed of quartz and feldspar (felsic). Impurities in within the minerals may give sandstone various colours, most common being tan, brown, yellow, red, grey, pink, white, and black.
Found in areas where erozion is fast or has been ongoing for a long time, in locations where sand particles and accumulate. Examples being around old river deltas, sandy deserts, and sandy beaches.
Economically sandstone is useful as a construction material. Sandstone formations often also house groundwater aquifers or petroleum reservoirs.
Mudrock
Composed of fragments smaller than sand particles. Mudrocks themselves are further divided into 4 categories by the size of the particles it is composed of. From finest to roughest, these are:
Claystone
Mudstone
Siltstone
Shale
Slate is a special type of metamorphosed mudrock.
Mudrock most often forms in ancient floodplains, ancient lakes, river deltas, near coastlines with coastal currents and good mud supply, and near glaciers. Mudrock needs quiet water conditions for deposition, which is a requirement for organic material deposition as well. As such, Mudrocks are likely abundant sources of petroleum and natural gas. Fossils preserve well in mudstones, so one can also expect mudstone formations to be important areas for paleontological study.
Biological Sedimentary Rock
Sedimentary rock composed of mostly organic matter. Examples include coal, (explained elsewhere) dolomite, and limestone, the last two of which are carbonate mudstones.
Carbonate rocks will be discussed in their own chapter.
Chemical Sedimentary Rock
Sedimentary minerals formed when mineral constituents of an aqueous solution become supersaturated and become to precipitate, forming solid compounds. The two most notable types of chemical sedimentary rock are Halite, better known as rock salt, and gypsum.
Metamorphic Rocks
Coal
Coal is a Sedimentary Rock and has many types. Coal is great for heating, and industrial uses.
What makes coal?:
Coalification: The formation of coal by the gradual heating and compression of organic matter, normally via peat. This is part of metamorphism. (See above for what that is.
Types of Coal
Peat is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. It is essentially coal before coalification, but can still be used for heating, it's just not that good at it.
Lignite is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It burns rather dirty. It has a carbon content around 25–35%,and is considered the lowest rank of coal due to its relatively low heat content. Accounts for 17 percent of the world’s coal reserves IRL.
Sub-bituminous coal is a lower grade of coal that contains 35–45% carbon. It burns rather cleanly too unlike Lignite. It ranges between Lignite and Bituminous This type of coal makes up 30 percent of the world’s coal reserves IRL.
Bituminous coal is a dense sedimentary rock that is the most common type of coal at 52% and is around 85% carbon at its best. There are two types, Metallic and Thermal.
- Metallic is used for Coking. A good coking coal must have excellent agglomeration properties, a high carbon content, and a low content of sulfur, phosphorus, and ash. The best unblended coking coal is high quality medium-volatile bituminous coal. Coking is extremely important as an industry.
- Thermal lacks the qualities to be used for Coking.
Anthracite coal is The King of all Coals. Anthracite is the most metamorphosed type of coal (but still represents low-grade metamorphism), in which the carbon content is between 86% and 97%. Very uncommon. Anthracite accounts for about 1% of global coal reserves.
Worldbuilding Note: Keep in mind these percentages whenever you claim to have a certain type of coal. Almost no one will have Anthracite coal for example.
Where do I find coal?
Coal in some form can be found about anywhere, but it is important to note that how much coal you have can vary and how well you can extract it too. If your rocks are sedimentary largely, you will likely have coal seams in them but I cannot by any means tell you where exactly things are because of a lot depends on the geology of the past. I recommend just looking up IRL where coal is often found and draw your own conclusions from there. Your nation will most likely not have enough coal to self-sustain itself and will need to import. Some nations will be loaded with it however.
Ores
Iron
Coal and Iron go hand-in-hand. Iron is a rather common resource, but unlike a certain block game, is not a singular thing at all. There are different types of Iron and historically Iron has drawn from different sources. The fraction of iron that is in Earth's crust only amounts to about 5% of the overall mass of the crust and is thus only the fourth most abundant element in that layer (after oxygen, silicon, and aluminium).
"Prior to the industrial revolution, most iron was obtained from widely available goethite or bog ore, for example, during the American Revolution and the Napoleonic Wars. Prehistoric societies used laterite as a source of iron ore. Historically, much of the iron ore utilized by industrialized societies has been mined from predominantly hematite deposits with grades of around 70% Fe. These deposits are commonly referred to as "direct shipping ores" or "natural ores". Increasing iron ore demand, coupled with the depletion of high-grade hematite ores in the United States, led after World War II to the development of lower-grade iron ore sources, principally the utilization of magnetite and taconite." - Wikipedia
Types of Iron
There are too many types to list but I will briefly address the main types. Note that Banded Iron Formations haven't been discovered yet. (1844 IRL) Lower-grade sources of iron ore generally require beneficiation, using techniques like crushing, milling, gravity or heavy media separation, screening, and silica froth flotation to improve the concentration of the ore and remove impurities. The results, high-quality fine ore powders, are known as fines.
Bog Iron is a form of impure iron deposit that develops in bogs or swamps by the chemical or biochemical oxidation of iron carried in solution. Due to its easy accessibility and reducibility, bog iron was commonly used for early iron production. It fell out of fashion come the middle ages, but was still used.
Laterite and other Sedimentary Rocks can have traces of Iron in them that can be extracted.
Hematite
Copper
Copper was the first metal used in mass by humans, and is still to this day an important industrial metal. Copper is an important industrial material used in many things, and is a wonderful alloy. Copper is the 25th most abundant element in Earth's crust, representing 50 ppm compared with 75 ppm for zinc, and 14 ppm for lead.
Types of Copper
There is no point in listing the types of copper there are because there is so many. But