This is only opinion, but if you are calling all the dark lines, mineral streaks, I believe that is the grain. If the grain has waves and twist in it, it will probably appear complicated if there is a straight(ish) saw cut through it.
I believe true mineral streaks are events that happen to the growing tree and then it reverts back to normal growth. This stick looks like normal growth happened in a possible consistently higher mineral environment, in either case, I believe minerals would deposit along growth rings, not off of growth rings.
I believe at the wrist, this wood was basically cut parallel to the grain, where if the growth rings showed, the cut would have likely had to have happened at or closer to 90* to the growth rings. I believe the islands of black coloration are areas where stock contour crossed, basically parallel, into and out of the plane of a growth ring. The grain appears to twists so that other areas of the stock show grain that has varying degrees of entering the stock approaching 90*, which would visually appear as a thinner and sharper streak.
This assumes that there hasn't been any grain enhancement techniques, and it appears as if someone did some manipulating of this stock. I think this type of wood appearance generally comes from the lower stump/root area. All just opinion and no better than others who probably know better. The sample stock has some eye catching grain, but I don't perceive it as a particular good blank. I do though think that the original stocker tried to layout with some intention.
