Nephrite jade is formed by very fine tighly felted fibres of tremolite and actinolite. Both also form marco crystals as well, and when formed as long fibres are types of asbestos. But we are interested in nephrite jade here which is cryptocrystalline tremolite and actinolite fibres felted together. The cutting quality of the jade is determined (1) the degree of felting; (2) how fine or coarse the crystals are; (3) whether the fibres are orientated in layers or a particular direction or it the felting is even in all directions. This determines how 'cuttable' the jade is, grading from finely felted with no directionality/schitosity which is a pleasure to cut) to poorly felted or felted in layers (schistose) jade that is difficult to cut and at worst is a crumbly uncuttable mess. All nephrite jade falls somewhere between these to extremes.
To determine the cutting quality (not colour quality of the jade):
Have a good look at your block, especially the uncut outside edges, is there any obvious "direction" in the stone, ie: visible layering or schisticity in the stone or any obvious chipping or are the fractures if present aligned in a particular way. Also if there are cut faces, do they look almost polished/glazed or are the faces grainy. Also look closely at the cut edge especially if there are two cut faces at 90 degrees, is the edge chipped and bumpy or is it razor sharp? If you hit a small chip with a himmer does it disintegrate or fracture into layers or resit destruction?
High quality AAA jade (based on the degree of felting not colour) is well felted in all directions with very fine fibres/grain. All cut faces will look almost polished, and the cut edge on the side of the slab will be razor sharp with no chipping at all. If your jade is like this the material will carve extremely well and can be cut in any direction you like, indeed it will be very hard or impossible to tell its orientation. This is the stuff to look for.
If it is good but not fine quality, there will be some 'directionality' in the jade. On an uncut block look for any fractures or shaters, if they are made up or 100s of tiny oriented fractures that is a sign that it is grainy. On a cut block you will notice chipping on one edge, while another edge is razor sharp. Also one cut face my look grainy or matt while the other looks polished. Another sign when cutting the jade will be that one corner of the cab or carving will continually chip or shatter while the rest is nice and clean and sharp. This is a sign that the felting is oriented in a particular way, this is called the "grain" of the jade. Generally slabs are cut lengthwise along the grain. If cut across the grain, especially thin slabs they are prone to snapping. Much of the BC jade is quite grainy and needs to oriented well before cutting. When cutting this jade you may find it chips on one corner every time the hard wheel hits that exact sport or angle, this quality of jade can still be cut well, just use soft wheels when cutting the corner that is chipping and use hard wheels for the rest.
Some nephrite jade (such as the Pakistan/Afghan jade and low grade ig Sur) is very schistose, the fibres are orientated in very structured layers rather than felted in all directions. This jade will often have a visible layered look and will chip very badly on cut edges with the chips disintegrating into thin layers. This stuff is poor quality jade (regardless or colour) and at its worst uncuttable. It can be tumbled with success, hence the big Pakistan jade tumbles on the market and the frequent tumble polishing of lower quality (schistose) Big Sur jade.
Some miners, catalogue all the stone they mine by painting an identifier on each block, they also paint on a code to show the orientation of the jade in the ore body, if your jade has this that will give you a useful guide for orientation.
Good luck cutting your jade.
David
