Hawaiian Koa wood characteristics?

I wanted to make some pens out of Hawaiian koa wood, so I bought a few blanks off ebay. I've never worked with Koa before, but the blanks seemed unusually lightweight. I read online that it's a medium density wood similar to walnut, but I can tell very easily that they are not the same weight. Here's a picture of the blanks:



So do you guys think this is really Koa?