A method of determining the morphology of cokes and chars_by analyzing the microscopic cross-sections of a sample from one microscopic view of polished blocks embedded in the polymeric resin according to the well-known methods, wherein the method comprises the steps of: a) taking one magnified photomicrograph by using a microscope with in a reflected, polarized light using λ retardation plate or the differential interference contrast, b) cropping the image to generate the view consisting the individual optical texture identified according to the ASTM D5061-07, called sample image, c) dividing the sample images into segments, using a mesh of a predetermined size to obtain the gradient measurement points d) measuring the direction and value of a grey colour gradient vectors for every gradient measurement point, using the edges detection digital method, to create the gradient histogram, putting all of the vectors from one sample image together, according to the rule that the middle of each vector is placed at the beginning point of the coordinate system, e) calculating the ellipse with a and b axes, where a>b, using the shape of the histogram as a base to define the shape of ellipse, f) calculating the fibrosity index W i as W i = (a-b)/a g) calculating the mean value of the fibrosity index as a dimensionless value within the whole sample using the additivity law, where the textures content measured according to the ASTM D5061-07 classification, is a weight in the equation, W x = ∑x i × W i, where x i is the volume content of the optical texture type and W i is the fibrosity index of an individual texture type, h) however the texture classified as filler phase texture, according to the classification from ASTM D5061-07 should use fibrosity index W i the same as calculated for isotropic texture, in calculation of W x. a) taking one magnified photomicrograph by using a microscope with in a reflected, polarized light using λ retardation plate or the differential interference contrast, b) cropping the image to generate the view consisting the individual optical texture identified according to the ASTM D5061-07, called sample image, c) dividing the sample images into segments, using a mesh of a predetermined size to obtain the gradient measurement points d) measuring the direction and value of a grey colour gradient vectors for every gradient measurement point, using the edges detection digital method, to create the gradient histogram, putting all of the vectors from one sample image together, according to the rule that the middle of each vector is placed at the beginning point of the coordinate system, e) calculating the ellipse with a and b axes, where a>b, using the shape of the histogram as a base to define the shape of ellipse, f) calculating the fibrosity index W i as W i = (a-b)/a g) calculating the mean value of the fibrosity index as a dimensionless value within the whole sample using the additivity law, where the textures content measured according to the ASTM D5061-07 classification, is a weight in the equation, W x = ∑x i × W i, where x i is the volume content of the optical texture type and W i is the fibrosity index of an individual texture type, h) however the texture classified as filler phase texture, according to the classification from ASTM D5061-07 should use fibrosity index W i the same as calculated for isotropic texture, in calculation of W x.