This paper is called silk paper and they are listed in the revenue section of the Scott Specialized. Granite paper is a different type of paper, although it does have many fibers as well. The fibers in granite paper are much more "squiggly" for lack of a better word and are usually both red and blue. It also has a lot of fibers, many more than silk paper, which only has blue fibers which usually appear as they do here in this typical example.
This is not the experimental silk paper, it is the regular silk paper. Experimental silk paper only has a very few threads and they are all short and straight. This paper was used for some years at the very end of the Joseph Carpenter contract (Butler had died so it was no longer Butler & Carpenter), during the ABNCO contract, and for a very brief time at the beginning of the BEP printings (depending on exactly which stamps were being printed at that moment).