If you have a cobble that is water worn you are ahead of the game.You need to identify the schistocity .Some jsdes are very uniform and the schistocity is of little importance but with others it is crucial to understand how bad the schistocity may become. The broad flat surfaces of a cobble are normally 90 degrees to the schistocity, that is if you are looking at the flat area of a cobble rotate it first to the side then to the narrowest point on the side. It is normally the narrowest because the schistocity is so well developed.Look for layering and look hard.If the piece is very schistose you need to be showing the flat area of the cobble and minimize the thickness of the piece. Very aggressive wheels will develop the schistocity as will hitting the pieces with a hammer.Acut piece with no natural surfaces can be examined for schistocity as well.Some jade will show slight veiling when it comes off the saw as the saw will develop the schistocity in some jades. Using a 30 or 60 grit hard wheelon the corners of a piece will chip the spot if the shistocity is well developed. These brittle jades can be fine but you must be very careful and try to avoid harsh grinding. If all you have is your eyes wet the preform and rotate it looking for layers. All jaes have inclusions to a degree and they lie within the schistocity plane.If the slab - preform was cut incorrectly you will be plagued with the schistocity on the front surface of your piece. With very uniform jades this is no problem but most jades of reasonable cost are a risk.Because of the natural shape of a jade cobble it fits in the saw easily to cut it incorrectly.To cut along the face of the cobble which is preferable takes some planning and preliminary cuts.
