Variations within species and woods: Wood varies greatly in weight and strength. Young trees of moderate to rapid growth have reddish heartwood and are called red fir. The narrow-ringed wood of old trees may be yellowish-brown and is known as yellow fir.
Hardness (Janka): 660; 49% softer than Northern red oak.
Dimensional Stability: Above average (change coefficient .00267; 28% more stable than red oak).
Durability: Durable but easily dented. Somewhat brittle and splinters easily, especially with age. Used for flooring, but may not be suitable for all applications due to its softness.
Sawing/Machining: Harder to work with hand tools than the soft pines.
Sanding: Sands satisfactorily.
Nailing: Good holding ability.
Finishing: Some boards develop a slight pinkish to bright salmon color when finished with some products. Because of tendency toward color change, care must be taken to avoid oversanding when refinishing an existing floor.
Comments: Sometimes milled for flooring as end-grain block, which is significantly harder than Plainsawn.
Information is from The National Wood Flooring Association
"Wood Species Used in Wood Flooring"