Google's Gary Illyes said on Twitter that Google still only has one index, a desktop index. There is no index just for mobile friendly web pages.
He said this in response to a feature request in Google Search Console to show a filter in the index status report for desktop index versus mobile index. Gary responded, "no, that wouldn't make much sense at the moment since we only have a desktop index."
Here is the tweet:
Gary said some time ago that Google is working on a mobile index but I guess that has not surfaced yet or will not be surfacing in the future?
Google not having a mobile index is an important concept for SEOs and Webmasters to grasp.
Forum discussion at aTwitter.