Many scientists believe that the mineral content in sedimentary rocks is mainly represented by magnesium, aluminium, fluorine, oxygen and silica. In 2011, a team led by the authors identified a small quantity of the rarest mineral in sedimentary deposits called dolomite, a compound comprising magnesium and various rare earths. Their study revealed that only a rare fraction of this mineral was associated with the mineral grains, which are considered as the building blocks of sedimentary rock.
Why mineral content alone can’t tell us where it came from. We know that one rare mineral is probably in hundreds of milligrams of water. We don’t know if that same mineral was on top of the sea floor, in the soil, on the plants or even in the air. We only know that it was in sedimentary rocks. In other words: we don’t know.
I’m talking about what is known as “detrital deposits”, deposits in which we know, quite correctly, that they are not a deposit in the original rock, but rather a geological anomaly. This is because we know it is much more likely that some mineral will migrate through the strata from inside to outside the rocks than vice versa.
Detrital sediments – what is detrital and what are your questions? Old blog: What is a detrital sediment? Detrital sediments are deposits with an extremely low concentration of water-soluble elements and are therefore considered to be detrital. They are not formed by the erosion by water, but rather by the movement and weathering of a thin organic crust below a bed of rock.
You’ll also see that most detrital sediments are low content. That means that their mineral content is quite low. We know that if they aren’t a detrital deposit they are probably not in the original rock, but rather in a secondary source. In other words, they were formed by some process of erosion during the long life of the sediment. To give an analogy to detrital sediments: This is a huge boulder.