Dear Mr. Saparin,

I investigated graptolite shales of Silurian and Lower Devonian age.

The only way to come to a sound conclusion is the use of reflectance measurements. Metamorphic bitumens from epi- to kataimpsonite have different reflectivity values (R’min- max %). This is also true for graphite and semigraphite.

Metamorphic bitumen:

5.2 to 8.8 kata-impsonite

2.0 to 2.5 meso-impsonite

1.5 to 1.9 epi-impsonite

Semigraphite:

Structure zone 6.84 to 6.86

Wall rock alteration 6.46 to 6.55

Graphite:

0.42 -7.60 to 0.30 - 9.5

I have to rub some salt into the wound. A precise differentiation between semigraphite and graphite can only be achieved by RAMAN and spectrocopic measurements.

DILL, H.G., KUS J., GOLDMANN S., SUÁREZ-RUIZ  I., NEUMANN T., and KAUFHOLD S. (2019) The physical-chemical regime of a sulfide-bearing semi-graphite mineral assemblage in metabasic rocks (SE Germany) – A multidisciplinary study of the missing link between impsonite and graphite. International Journal of Coal Geology 214:

Can you provide me with diagenetic or metamorphic data. Is the graptolite shale overcooked ? Based upon that data you cannot determine what the OM is but constrain the PT regime and you get an idea of the carbon modifications on an indirect way.

I suspect of conducting a maturity study whether the black shales are oil-, gas-prone or barren as source rocks

DILL, H.G. (1986) Metallogenesis of the Early Paleozoic Graptolite Shales from the Graefenthal Horst (Germany). - Economic Geology, 81: 889-903.

DILL, H.G. and NIELSEN, H. (1986) Carbon-sulphur-iron-variations and sulphur isotope patterns of Silurian Graptolite Shales (Germany). - Sedimentology, 33: 745-755.

DILL, H.G. and PÖLLMANN, H. (2002) Chemical composition and mineral matter of paralic and limnic coal types of lignite through anthracite rank. Upper Carboniferous coal in comparison with Mesozoic and Cenozoic coals (Germany).- Canadian Society of Petroleum Geologists  Memoir, 19: 851-867.

All publications are available on the Researchgate Server on request.

If you want to get closer to coal petrography see the textbook of:

Taylor, G.H., Teichmüller, M., Davis, A., Diessel, C.F.K., Littke, R., Robert, P., 1998. Organic Petrology. Gebrüder Borntraeger, Berlin-Stuttgart, 704 pp.

There you might find some more pictures which help you come closer to a solution for your problem.

H.G.Dill

Unfortunately, it is not possible to unequivocally identify this substance based on your photos alone. I interpret that substance as pyrobitumen or graphite. Graphite can be easily determined with a polarizing microscope, if you have a polished section. Another determining criterion is the deformability of the substance. With the help of a pin, the scratch test shows whether the substance disintegrates brittle (producing angular fragments) or whether it is ductile and plastically deformed. Another solubility test can show whether the substance dissolves in gasoline or not. Quasi-crystalline pyrobitumen (variety "tucholite") is not soluble in gasoline.

Try it, it works. Good luck!

Best regards,

Guenter Grundmann

Dear Mr. Saparin,

I investigated graptolite shales of Silurian and Lower Devonian age.

The only way to come to a sound conclusion is the use of reflectance measurements. Metamorphic bitumens from epi- to kataimpsonite have different reflectivity values (R’min- max %). This is also true for graphite and semigraphite.

Metamorphic bitumen:

5.2 to 8.8 kata-impsonite

2.0 to 2.5 meso-impsonite

1.5 to 1.9 epi-impsonite

Semigraphite:

Structure zone 6.84 to 6.86

Wall rock alteration 6.46 to 6.55

Graphite:

0.42 -7.60 to 0.30 - 9.5

I have to rub some salt into the wound. A precise differentiation between semigraphite and graphite can only be achieved by RAMAN and spectrocopic measurements.

DILL, H.G., KUS J., GOLDMANN S., SUÁREZ-RUIZ  I., NEUMANN T., and KAUFHOLD S. (2019) The physical-chemical regime of a sulfide-bearing semi-graphite mineral assemblage in metabasic rocks (SE Germany) – A multidisciplinary study of the missing link between impsonite and graphite. International Journal of Coal Geology 214:

Can you provide me with diagenetic or metamorphic data. Is the graptolite shale overcooked ? Based upon that data you cannot determine what the OM is but constrain the PT regime and you get an idea of the carbon modifications on an indirect way.

I suspect of conducting a maturity study whether the black shales are oil-, gas-prone or barren as source rocks

DILL, H.G. (1986) Metallogenesis of the Early Paleozoic Graptolite Shales from the Graefenthal Horst (Germany). - Economic Geology, 81: 889-903.

DILL, H.G. and NIELSEN, H. (1986) Carbon-sulphur-iron-variations and sulphur isotope patterns of Silurian Graptolite Shales (Germany). - Sedimentology, 33: 745-755.

DILL, H.G. and PÖLLMANN, H. (2002) Chemical composition and mineral matter of paralic and limnic coal types of lignite through anthracite rank. Upper Carboniferous coal in comparison with Mesozoic and Cenozoic coals (Germany).- Canadian Society of Petroleum Geologists  Memoir, 19: 851-867.

All publications are available on the Researchgate Server on request.

If you want to get closer to coal petrography see the textbook of:

Taylor, G.H., Teichmüller, M., Davis, A., Diessel, C.F.K., Littke, R., Robert, P., 1998. Organic Petrology. Gebrüder Borntraeger, Berlin-Stuttgart, 704 pp.

There you might find some more pictures which help you come closer to a solution for your problem.

H.G.Dill

Guenter Grundmann Thanks for the suggestion. I agree that either pyrobitumen or graphite would be a good start. The photomicrograph is from a polished block and I will check again if it could be a graphite.

Harald G. Dill Thanks for the detailed response and list of helpful references. The Ordovician-Silurian graptolithic black shale sampled had abundant graptolites. The morphology of graptolite fragments is easily identified: solid grey-white under non-polarized light, show traces of fusellar layer and anisotropy under polarized light. Graptolite reflectance is Ro (%) 1.7-3.0 (mostly observed perpendicular to the bedding). Pyrite, when present had a very high reflectance. The pictures I've uploaded however, had a rather chaotic, flaky/broken-like texture inside, with Ro(%) less than 4.0 and I have not seen much of it in the papers I have read so far. I will see if I could find some more pictures from the literatures you have provided.

best regards,

Aqqid

I do not know how and how precisely your reflectance measurements have been carried out. Given a spread from 1.7 to 4.0 % Ro covers the states: low volatile bituminous, semi-anthracite and anthracite. In other words it is highly coalified matter , neither graphite nor bitumen. The system seams to be rather overcooked.

The graptolite shales (rather call them slates) I investigated contain 2-10 % TOC. The vitrinite reflectance measurements brought about 3 different types of OM:(1) detrital semigraphite, (2) graphite and (3) metamoprhic bitumen (meso to kataimpsonite) (type: alum shale - hosted metal deposits of low-grade- large tonnages, which were mined near Gera-Ronneburg in the former GDR for U). These environments and the resulting rocks are good for the metallogenesis of U, V, Ag, base metals, Sb and, in places Au, but not for HC. The argillaceous rocks were submitted to low-grade - (very-low grade) metamorphic conditions which are above range where you can expect HC relevant plays.

Your reflectance data should direct your ideas to the textbook on coal which I cited in my post above.

I think that the white elements be able to correspond to vitrinite of high reflectance possible anthracitic. The bright round points around the central part can be pyrite.