Is silk and wool shatnes?
No it is not shatnes. The Mishna (Klayim9-2) says that silk and wool are not klayim (shatnes) however they should not be woven into each other because silk looks like wool and flex. Therefore it is maris ayin, because people will think that they are seeing a mixture of wool and flax. The meforshim comment that nowadays there is no fear of people mixing up the appearance of silk with wool or flax, since silk is very common among us, therefore there is no problem with having them in the same garment. Therefore it is not an issue.
Rosh (Nida chap. 9-7), and the Rav (Bartenura) Klayim 9-2, Shulchan Aruch Y:D 298-1, also see O:CH 147-1.