Jadeite has rounded edges, almost impossible to get a crisp edge, while nephrite will have crisp edges. Both are very hard (jadeite is harder) but easy to carve with modern diamond cutting tools. Old jadeite is valuable in part due to the thousands of hours that were spent to carve it using grit or sandstone. Takes a real expert to spot a modern copy imitating an old piece (and with 100x difference in value). Personally I prefer the cheaper nephrite from NZ (where there is no jadeite) which often has great beauty but not investment grade as jade has been in the past (not sure about future appreciation though).