The matrix of your wood appears to take on the look of walnut, olive wood or perhaps a burl, but the grain does not appear to be anything similar to lignum vitae. (Some of the lignum vitae installed originally in the Hoover dam is supposedly still there). regardless of the wood, that #19 has an extremely cool handle! Good luck with it.
Best, Capt. Chris
P.S. I have a small piece of "Curly Koa" which has similar properties to your handle. I'll post some, if I "EVER" get a break in this friggin' weather!!...CCS