One of the early patented doorknob designs. Made of composite material. The Westlake Design Black by the Dibble Mfg. Co. dates to 1877. Considering that this knob is approaching 150 years old it's in amazing shape. While probably not rare when you look at how well these are made and how well they held up, if you're restoring an old home with these or are a collector looking for a match to your knob I would imagine these are not that easy to locate.
While not about this particular knob, if you would like more information on composites, there is an excellent article about them in "The Doorknob Collector) newsletter #141 from January/February 2007 that you might enjoy if you Google it.
T-204