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What sedimentary rocks are unlikely to form? What minerals are not "good" for forming?

The earth is REALLY into balance in all things. This includes the stability of minerals and their susceptibility to surface weathering processes. There is so much of how the earth works wrapped up in mineralogy that the discussion could go in for a very long time. In this case we're mostly concerned with the effect of chemical weathering on minerals which are brought to the surface of the earth. Sedimentary rocks are formed from sediments formed and deposited at or near the surface.

Most minerals are formed at some depth within the earth, and when they are moved closer to the surface it results in a subtle to profound change in environment. All known minerals can and will be attacked by chemical weathering when exposed to moisture, heat, and time (remember the 4th Law of GeoFantasy). A key factor is the time - not all minerals are equally susceptible, and therefore weather at different rates. Quartz, for example, is so nearly inert that it thwarts the chemical attack, and ends up as sand for the beaches. The chemical attack actually changes the minerals - the original stuff is gone, with new minerals forming in their place. Many of these secondary minerals are clay. Clay is real small, and mostly floats out to sea, forming vast sedimentary deposits on the seafloor. In addition, many sedimentary rocks, both marine and continental, are composed of calcium carbonate in varying amounts.

So I guess the short version to "what minerals are not 'good' for forming?" would be: anything other than quartz, clay, and calcite. Sure, lots of other minerals end up in sedimentary rocks, but in many cases they are only temporary. Over the course of geologic time they will continue to adapt to a constantly changing environment.


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