This is the first marble I’ve ever tried. The initial fractal shape is easy to get down, but marble also has varying levels of depth where the minerals get more difficult to see. I essentially took a noise, selected segments of it, and blurred each segment a little more or less than the other to get that look. The white line pattern was achieved through making a custom voronoi pattern; make rectangles in a tile generator and plug it into a Distance node. Then, do an edge detect on that and you get the basis for the line pattern.