The yarn is Socrates, by Alpaca with a Twist. I got it at the Knitters' Day Out market last September. It is 30% Baby Alpaca/30% Merino Wool/20% Bamboo/20% Nylon in a heather-y blend. It is super soft and downright dreamy - a little splitty, but I can deal with that. It's so soothing to work with.
The pattern is Shadow Rib, from Charlene Schurch's The Little Box of Socks. You know how fond I am of rib variations on a sock.
Mmmm, look at that stitch definition!