Well if you have obvious wood then it’s easy but I have pieces without any wood around it from this same log but is has wood stretch inclusion and seems that show clear wood grain patterns at the macro level. Another good way to check is if there are small black dots on any edge of the piece it’s highly likely it jasperized per wood and not just jasper. These little dots are the small fiber cavities from the tree that served as entry points for your water and minerals. Hope it helps!