1. AuctionsThe mines of Golconda, India, have produced some of the world’s most famous gems: the Hope, the Koh-i-Noor—and the appropriately named 52 ct. D-color internally flawless Golconda. On Dec. 10, the eponymous stone hit the auction block at ­Christie’s New York and fetched an impressive $10.9 million, or $207,600 per carat—just the latest eyebrow-raising hammer price in a year full of them.2. PartnershipsBlue Nile took a surprising step into the non-cyber world with its holiday venture: a Wedding Suite at Nordstrom’s Seattle flagship featuring more than 150 Blue Nile ­engagement and wedding rings. While the e-tailer doesn’t sell diamonds at Nordstrom—a rep directs shoppers to BlueNile.com—the venture may be seen as a tacit admission that brick-and-­mortar stores enjoy some advantages. “Some customers want to get up close and personal with jewelry before buying