Santos Rosewood (Machaerium or Scleroxylon), also known as "Pau-Ferro," is a subspecies of the 'Machaerium' family, and is not a part of the 'Dalbergia' sub-species (commonly known as Rosewood).
"Pau Ferro" is a distinctive and beautiful wood, with so many of the characteristics of Brazilian Rosewood that is regarded as such by many luthiers. It's stable, abrasion resistant, hard, attractive, exotic, and has good compression strength parallel to the grain. All of this makes it very suitable wood for fingerboards and acoustic backs. Moreover, Pau Ferro does not require any finish, and for this reason is also used for necks - allowing a natural, silky touch to the hands of the player, thanks to its waxy feel.
Visually, Pau Ferro ranges in color from a light violet brown to reddish brown to dark chocolate brown, with occasional olive and black streaks. Finer in texture than most rosewoods, it is a close visual substitute for East Indian Rosewood and has very similar tonal properties: rich, powerful basses and very prominent overtones. In some cases may be slightly brighter, allowing for a more open tone.
It is also used for similar purposes as Brazilian rosewood, such as turnery, cabinets, fine furniture, specialty items, and decorative veneers.