Walnut (American Black)
Variations within species and grades: Great variety of color and figure within species, as well as variation in color among boards, especially in lower grades and from material that isn't steamed prior to kiln-drying.
Hardness (Janka): 1010; 22% softer than Northern red oak.
Dimensional Stability: Excellent (change coefficient .00274; 26% more stable than red oak).
Durability: Moderately dense, very strong, good shock resistance. Not as dent-resistant as oak.
Sawing/Machining: Easily worked with hand tools, and has excellent machining qualities.
Sanding: Sands satisfactorily.
Nailing: Fair resistance to splitting; good holding ability.
Finishing: Finishes nicely, with a handsome grain pattern.
Comments: Distinctive sweet aroma when worked. Frequently used as a highlight material for borders or other inlay techniques.
Information is from The National Wood Flooring Association
"Wood Species Used in Wood Flooring"