I have got the minerals content of sedimentary rocks via XRD analysis, and want to give the rock types to each sample. The samples were collected from Miocene and Oligocene in a single well, which were fine grained in thin section analyses. The clay content was 5-55%, and some samples contained as high as 50% carbonates. Mainly, I have categorized them into three groups based on detrital minerals content: a) less than 50%, b) 50~75%, c) more than 75%. Group a can be named as mudstone, and group b named as argillaceous siltstone. What is the name of group b in English?
Many thanks to you.
With sedimentary rocks the mineral composition is one thing. If there is a visible grain size with such a high quartz and feldspar content you are likely dealing with a sandstone of marine origin. Any decent petrology book should be able to cover this.
I agree. However, some rocks even if one can see the grains may require XRD to determine grain composition.
Kenneth, thank for your suggestion. I have not got the copy of Francis Pettijohn's 1957 book, but got the edition of 1949. Like many other traditional sedimenray books' description (both in English and in Chinese), there is no unique classification method based on minerals content.
To Jeffrey's opinion, I think the visible mineral content is much less acurate than XRD as Kenneth said "they are not the same".
As many different criteria of lothology have been given based on different aspects, I think the one has to select a criterion for his/her own thoughts.
Another question, can I use the argillaceous-bearing siltstone as the name of group b? or is mud-bearing better?
Kenneth, what is the names of the rock type if you have to give?
it is sure that there is difference in XRD and petrographic microscope analysis. And here we want to categarize them just based on detrital minerals content. The samples were actually fine grained source rocks in the thin section analyses, so we can call it mudstone or siltstone.
I think I was misunderstood. Even if one can see the grains, XRD may sometimes be necessary. What I was getting at is that in sedimentary rocks composition is one element and grain size is another, The question does not indicate grain size. only tht constituents were identified by XRD, Fine. But then based on this composition and the grain size one should easily be able to name this rock type. Since it is fine grained and high in feldspar, this seems to indicate the feldspar has not altered to clay (??). If so then siltstone.
HA, it becomes interesting. The samples were within Miocene and Oligocene. The clay content was 5-55%, and some samples contained as high as 50% carbonates. It is fine-grained source rock in a single well. I think two ends (one is detrital minerals, the other is clays) classification method could be accepted, do you agree? Here what I am puzzled is the name of the rock types in Eglish.
Sorry, Kenneth. The samples are in different members with different minerals content. Thank you all the same.
Dear Mr. Xiaojun Zhu ,
your information sounds for me a bit cryptic and maybe you can more precisely describe what your database is and what you are going to do. First and foremost XRD-based mineral quantification is not an easy task and taken to the extreme you might seek refuge to the Rietfeld-Method to obtain reliable data. Which approach have you taken? For the classification of detrital rocks I use the triangular plots. This is a classical one. As I told you please provide us with more data.
Best regards
Harald G. Dill
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