The S-7 borehole log from the Sumina area (USCB Poland) revealed the presence of three basaltic veins
originating from a basalt dyke. Coal interlayers in the rocks surrounding the basaltic veins have been coked to
form natural coke. Photometric measurements revealed that the optical properties of the studied natural coke
samples are characteristic of semi-graphite (Rmax > 9%). The natural coke matrix of all of the analyzed samples
has a biaxial negative optical character. Vitrinite in the examined natural coke samples is characterized by a
lower optical anisotropy than that of the natural matrix and it has a biaxial positive optical character. Vitrinite
in almost all samples taken at locations more distant from the intrusion has a biaxial positive optical character.
A reversal of the changes of the true maximum vitrinite reflectance and bireflectance with changing distance
from the second basaltic vein has been observed. The temperature regime that acted upon the dispersed organic
matter located in the immediate vicinity of the intrusion, estimated on the basis of the selected experimental
data, is suggested to be higher than 750 °C.