Books are always a good investment. That’s what shareholders of Barnes & Noble discovered as the company’s stock skyrocketed 95 percent before the market even opened Monday on the news that Microsoft had secured a 17.6 percent stake in the bookseller’s Nook business. Barnes & Noble announced in January that it wanted to spin off its e-book division. As part of the deal, Microsoft will include a new Nook application in Windows 8, a move that could open up Barnes & Noble’s product to millions of e-book readers. Shares of Barnes & Noble, valued at $13.68 before the announcement, leaped to $26.70 early Monday morning.