Android may be increasing its smartphone market share, but its gains are not coming at the expense of Apple, according to the latest report from Nielsen. In the third quarter, Android captured 43 percent of the smartphone market in the U.S., up from the 40 percent it held in the last quarter. Apple, meanwhile, held steady at 28 percent market share.

The overall smartphone market is bigger than it was three months ago, as 43 percent of mobile phone users now reporting that they own smartphones, up from the 40 percent who said they owned the devices earlier this year. This means that while Apple is being buoyed on a rising tide of smartphone ownership, it isn’t growing its overall market share. This is despite consumer surveys in the second quarter indicating that one-third of consumers who said they were likely to get to get a new smartphone wanted an iPhone. One-third said they wanted an Android device, while the remaining one-third were undecided.

Android’s rapidly growing market share seems to come mainly at the expense of RIM, which saw market share for BlackBerry devices dip slightly from 19 percent to 18 percent. Other platforms dropped to a four percent market share. Microsoft’s Windows Mobile also failed to capitalize on the growing market, sitting in a distant fourth place with 7 percent penetration.

While the smartphone penetration rate has increased in every demographic group Nielsen surveyed since the second quarter, the most enthusiastic adopters are still adults between 25 and 34. Sixty-two percent of consumers in that age group reported owning a smartphone in the survey. The fastest growing group of smartphone users were those between the ages of 55 to 64, where 30 percent reported owning the devices. That’s up five percentage points from July.