Stone or gem - Possible spoilers

From what I remember of the books, the only way to travel from one time period to another was by stepping between those huge, ancient, monolithic stones in places like Scotland, and it had to be done at specific times of the year, such near the Spring/Autumn Equinox, or the Summer/Winter Solstice. Diana Gabaldon does not specify in the books why some people can travel through time and others cannot.

The tv show changed this a little bit. In the tv version, you had to actually touch the ancient stones at those specified times of the year, and they hinted that you had to have magic in your blood, which is rare, but would explain better why some people could use the stones, and others could not.

In both the books and the tv show, there was talk of how time-travelers could sense a low "hum" in the stones at certain parts of the year, and that's when the "portals" between times were "open."

I haven't watched the more recent seasons, nor have I read any of the books beyond part of "Voyager," but last time I checked, you couldn't travel through time without those gigantic stones around.

I don't think it was in the books until Dragonfly in Amber when Roger and Brianna met Geillis in the 1960's and the three of them (Roger, Bri and Claire) read her journals. I wonder if that was something the author hadn't really thought about and chose to include after she wrote Outlander.

In the show, they threw in a couple of lines to kind of retroactively make it consistent. In the Season 2 finale, Jamie gives Claire his father's ring just before sending her back through the stones. In Season 3, Claire briefly mentions that when she went through the stones the first time, she was wearing a watch that had Jewels in it. Can't remember if she says that the jewels were missing or not, but when she arrived in the 20th century at the beginning of Season 2, the stone was missing from Jamie's father's ring.