Usage of Google’s mobile platform across the Millennial network doubled iOS in the third quarter according to new data just released by Millennial Media. After representing 54% of impressions served by the mobile ad network in August, Android finished strong to account for 56% of impressions in the September quarter. That figure doubled iOS in the No. 2 spot with 28% during the quarter, and it dwarfed RIM’s 13% share. Symbian accounted for just 1% of impressions and Microsoft’s Windows Mobile and Windows Phone platforms combined to also account for 1% of impressions. The iPad dominated tablets, having grown a whopping 456% between the third quarter in 2010 and this past quarter, and impressions across iOS grew 60% over the same period. Apple was the top manufacturer on Millennial’s network in the third quarter with a 23.09% share followed by Samsung (16.48%), HTC (15.5%), RIM (11.05%) and Motorola (10.7%). Apple’s iPhones were also the top handset line with a 12.55% share, more than double the No. 2 device line, LG’s Optimus phones, which accounted for 6.3% of impressions served. RIM’s BlackBerry Curve line was next with 4.7% followed by Motorola DROID phones with 4.35% and the HTC desire with 4.01%. Additional charts from Millennial’s third-quarter Mobile Mix report follow below.