Your pic #3 shows a highly irregular boundary suggesting that the stone has to be natural (or I'll eat my hat). It looks like the part of the mine where this thing came from had some slippage or faulting and/or was more highly metamorphosed than the other areas, resulting in this folding of the two strata. The round patches - and possibly the darker areas at the contact - may be areas of concentrated garnets. You can check with a handlens to see if you can find cubic crystals, or 12-sided critters in there. Nice looking stone....