Dear Mr. Fang,

I do not understand how you can dissolve inorganic carbon using hydrochloric acid as solvent. Inorganic carbon means graphite, semi-graphite, meta-anthracite and the various stages of impsonite (metamorphic bitumen) which are the most common constituents. None is soluble in the acid mentioned by you. Graphite ranks among the most inert substances and used to manufacture crucibles for chemical analyses. So the question concerning the organic carbon such as coalified matter , HER, LER ..etc. is in my opinion superfluous to be discussed. With HCl you can clean substances containing the inorganic compounds listed above from impurities like phosphates or carbonates but you cannot decompose the C-bearing substances.

There is something wrong (?)

H.G.Dill

Thanks for your answer,I'm sorry I didn't make myself clear.What I mean is 'removal of the carbonate component of the sedimentary rock with HCL'

Dear Mr. Fang,

I refer my post at the beginning. It depends on the type of OM which is a function of the source, diagenesis, metamorphic regime and hydrothermal/magmatic impact. It is first and foremost a redoxmarker pointing to reducing conditions. Any answer going beyond that would be a roaming around in a rather complex and large geochemical realm.

H.G.Dill

Dear Chenxi, thanks for asking this interesting technical question. As an inorganic chemist I can only support the first comment made by Harald G. Dill. Treatment of rock samples with hydrochloric acid will only remove / dissolve carbonate components, but various inorganic and organic carbon-containing components will remain. Graphite would be considered inorganic, while various coals and bitumen contain organic components such as e.g. hydrocarbons and high molecular weight phenols.

The most efficient tools to study the origin of the OM- bearing clastic deposits are the morphology and orientation of bioclasts combined with the LER/HER (=low exothermic / high exothermic reaction) ratio method to get an overview of the OM-bearing sediments. Further more detailed investigations measures should involve coal petrographic studies and spectroscopic ones to define the crystallinity of graphite, semigraphite, anthracite, meta-anthracite. The HER/LER approach also allows for a distinction of man-made organic compounds from sewage treatment plants. We used it only for a screening prior to a more detailed follow-up OM analysis of natural carbon-bearing material.

See the most recent approach in:

DILL, H.G., KUS J., BUZATU A., BALABAN S.-I. ,KAUFHOLD S., and BORREGO A. G. (2021) Organic debris and allochthonous coal in Quaternary landforms within a periglacial setting (Longyearbyen Mining District, Norway) - A multi-disciplinary study (coal geology-geomorphology-sedimentology).- International Journal of Coal Geology (on-line)