* I hope the following info on Electrical Deposition from Wikipedia may be helpful.
Electrophoretic deposition (EPD), is a term for a broad range of industrial processes which includes electrocoating, e-coating, cathodic electrodeposition, and electrophoretic coating, or electrophoretic painting. A characteristic feature of this process is that colloidal particles suspended in a liquid medium migrate under the influence of an electric field (electrophoresis) and are deposited onto an electrode. All colloidal particles that can be used to form stable suspensions and that can carry a charge can be used in electrophoretic deposition. This includes materials such as polymers, pigments, dyes, ceramics and metals. --- The process is useful for applying materials to any electrically conductive surface.
--- The coating process itself ... normally involves submerging the part into a container or vessel which holds the coating bath or solution and applying direct current electricity through the EPD bath using electrodes. Typically voltages of 25 - 400 volts DC are used in electocoating or electrophoretic painting applications. The object to be coated is one of the electrodes, and a set of "counter-electrodes" are used to complete the circuit. --- A baking or curing process is normally used following the rinse. This will crosslink the polymer and allows the coating, which will be porous due to the evolution of gas during the deposition process, to flow out and become smooth and continuous.
--- The primary electrochemical process which occurs during aqueous electrodeposition is the electrolysis of water. This can be shown by the following two half reactions which occur at the two electrodes:
Anode: 2H2O ---> O2(gas) + 4H(+) + 4e(-)
Cathode: 4H2O + 4e(-) ---> 4OH(-) + 2H2(gas)
In anodic deposition, the material being deposited will have salts of an acid as the charge bearing group. These negatively charged anions react with the positively charged hydrogen ions (protons) which are being produced at the anode by the electrolysis of water to reform the original acid. The fully protonated acid carries no charge (charge destruction) and is less soluble in water, and may precipitate out of the water onto the anode.
--- Non-aqueous electrophoretic deposition
In certain applications, such as the deposition of ceramic materials, voltages above 3-4V cannot be applied in aqueous EPD if it is necessary to avoid the electrolysis of water. However, higher application voltages may be desirable in order to achieve higher coating thicknesses or to increase the rate of deposition. In such applications, organic solvents are used instead of water as the liquid medium. The organic solvents used are generally polar solvents such as alcohols and ketones. Ethanol, acetone, and methyl ethyl ketone are examples of solvents which have been reported as suitable candidates for use in electrophoretic deposition.
* So an atmosphere containing methane might help electrical deposition.
* There are 3 kinds of sedimentary rock: sandstone, limestone and shale, each of which can be metamorphized. Metals tend to be electrically conductive, I think, so any rock containing metals should be fairly conductive. Clay contains aluminum and it forms shale and slate [metamorphic shale]. Aluminum is in granite and basalt etc. Sand can contain metals, but quartz alone, i.e. SiO2, has no metal, but some metals, like gold, are found in quartz veins. Limestone is mainly calcite, i.e. calcium carbonate, so I don't know that it's conductive, but it can contain impurities or be mixed with shale or sandstone.
Kapriel said: The presence of carbonate layers between sandstone "dunes' needs to be addressed
* What source are you referring to regarding carbonate between dunes? Is that calcium carbonate? Do you know what the usual thickness of the carbonate layer is?