I would like to suggest are slow baby step at a time look at geology.
How do geologists really know what a sample is and how it came to be?
Too often we seem to see very general terms used that then get qualified as a different term but without an explanation of what the differences are and why they are made. I'd like to see if by my asking question those good folk who actually know what they are talking about can 'splain it to me.
Hopefully we can move slowly enough to avoid gross generalities but still keep things simply enough that even I can understand them.
The discussion should move from general terms like sedimentary rock to more specific points like the basic methods sedimentary rocks get produced; to how specific designations are identified and what original materials produce specific final types of rock.
First I like to explore just sedimentary rocks before attempting to identify igneous or metamorphic rocks.
To begin, are all sedimentary rocks produced the same way?
Please, let's go slow and until I understand something put off new questions.
Before we move on to the biological sedimentary rocks can we spend a little more time at clastics? I know I'm slow but I still have a few more questions about identifying clastics before we move on to chemical and biological sedimentary rocks.
So clastic sedimentary rocks begin as other rocks and before they can exist there needs to be time enough to first weather and erode other rocks to make the small rock and mineral fragments that have been eroded and transported to a depositional center that edge mentions in Message 6.
That brings up a couple other points.
First it seems from what edge said we need two processes. We need weathering and erosion and then the pieces parts need to be transported to some spot where the stop and accumulate. To end up as a layer in the geological column of a given location the pieces parts need to stay in that location long enough for the individual pieces parts to turn back into another big rock.
And back towards mud. It seems that the size of pieces parts also plays some part in determining what the final clastic rock will become.
Is that correct and if so what types of clastic rocks are made from the different sized pieces parts?
How can someone tell the various resulting rocks apart?
We can make it more difficult by giving them modifiers like 'calcareous' or 'organic'; or we can combine the terms to things like 'sandy carbonaceous mudstone' (which may not actually exist, but you get the idea).
I think so but as usual, a few questions. I've seen things described as mudstone and siltstone but also as shale.
Particle size is pretty clear but what produces the different sized particles. Why does something end up as silt or mud or clay?
Where does shale fit in? What is it and why is it different? And then there is slate???????
Re: Great so far but I'm slow so humor me by expanding some.
Oh, I missed this. Slate is a metamorphic rock, and comes apart into layers because it has undergone foliation. To explain this, consider that the silicate minerals in a rock have shapes: they can come in strings or sheets. So when a rock is heated and compressed, these minerals get pushed so that they lie perpendicular to the direction of the compression.
So far we have discussed two kinds of rock that both are found to create layers, shale and slate. The later has undergone metamorphose and it was that process through crystal alignment that produced the layering.
Are the layering found is shale produced a different way?
For clastic sedimentary rocks to form there first need to be other rocks and those prior rocks need to get weathered and eroded into small pieces parts. The final material will be determined by what the original material was and particles size as well as crystalline structure. Some materials will also change form should they undergo metamorphose.
Back in Message 6 edge mentioned a second family of processes, chemical sediments that precipitate out of water such as chert, or evaporites, or travertine, or various types of iron formations. I imagine that for things to precipitate out they must first be suspended in water and so once again they must exist before they can be precipitated out.
Is that correct?
What is chert and travertine.
Would limestone and chalk fall in the clastic category?
Are the mineral salts examples of precipitates?
edge's reply while I was writing this adds another question.
What is the difference between lithification and metamorphism.