These NanTans are considered "core" material.  The iron has rusted away and the nickel core is left. Most have an interesting triangular crystal structure.  These are about the size of a pea and come in their own individual clear plastic box.

More "core" material.  Again, most have an interesting triangular crystal structure.  Sizes range from 6.7 grams (19mm x 14mm x 12mm) to 23.6 grams (26mm x 21mm x 16mm). Price is $2.50 per gram ($17 - $59).

These NanTans are thin slices of the regular chunks.  A little rust is showing, but can be cleaned up with amorall.