Agreed...Color, grain, sapwood is Black Walnut...If piece is completely dried, cutting into it to identify will produce a purple color still, if any "greenish moisture from sap" is still present, cut area produces a green color which can turn purple in less than 30 minutes. Especially in Summer sunlight or heat. Simple test, plane it with a hand planer, shavings should pruduce a brownish purple color under shaved area. Bark is... however, similar to that of a Black Locust, however a Black Locust will have a lighter brown/gray bark, rather than the Black Walnut which has a medium to dark brown/grayish bark. (There is only one other tree in the world that cuts green color and turns purple, it's Purple Heart & grown in Brazil. (Sapwood on Purple Heart is green)
It will burn just as good as red oak, and will produce popping if green or seasoned & water wet, similar to popping of 1st Generation Seasoned Cherry.
Buzz is correct in this test, Walnut has a specific smell, none like any other due to the toxicity level of the timber. Generally the ground surrounding a Black Walnut is toxic as well, therefore rendering the soil poor quality for growing other plants below them (similar to Cedar). Shavings of Black Walnut are very toxic, DO NOT put shavings in a barn with Horses, the toxicity will enter into the horses hooves and eventually kill the horse. Wear proper respirators when milling, planing, cutting and sanding Black Wanut due to it's toxicity. toxicity is similar to Mahogany.
I also agree with cj, I too cut it and mill it all the time, currently I have over 300 LBF in the attic drying, I know BW! If you still are not convinced, ask the guy you got the pieces from and ask him to show the exact stump spot it came from, then kick around in the leaves on the ground until you start kicking up large green/black balls that dye your tan boots a greenish/black...those are the Walnuts themself!
The only other possibile tree it might be is 'Popular' as it when dried does have purple and green colors, however...the pics submitted have grain of Black Walnut, not Popular.