It can be seen as a cross between Obsidian and Flint, so it is a great choice as a happy medium. Dacite is opaque to very slightly translucent, medium gray to black in color and is slightly grainier than glassy obsidian. It does look more like stone than obsidian. This is what happens to obsidian when nature cools it more slowly.
Our Dacite spalls are on the small side more for arrow points than knives. Although you could make a knife from some of the larger pieces. They can vary from a couple inches to over four inches. They're pre-bagged and sold by the pound, so expect a good mix of the various sizes.