I had alot of fun on this site and the hardest part was narrowing down my choices. I came on to buy some marbles for my own son and ended up purchasing materials that I will use with my whole cub scout den.
Size is as-packaged, or the diameter of loose marbles. ("D" is the diameter of round items other than marbles.)
Wurlitzer has a zig-zaggy twisted core of dark yellow, red, and dark blue, on a white core. The core is encased in crystal clear glass topped with black lines mirroring the zig-zag core which creates a great sense of depth.