I read it as the vein having been exposed by the movement of the glacier advancing, taking everything that was previously above the vein with it and exposing it

I read it as the vein having been exposed by the movement of the glacier advancing, taking everything that was previously above the vein with it and exposing it to the surface. I didn't think the glacier was necessarily present in 5900 BC. Now that I've gone back and re-read the article, it looks like I was mistaken: > [H]e came upon a rich vein of rock crystal exposed by a retreating glacier. > The team determined that hunter-gatherers living during the Alpine Mesolithic period (ca. 9000–5500 B.C.) visited the site as recently as 5900 B.C. and extracted rock crystal from the vein, after which it was covered by the advancing glacier. The article seems to be saying that the glacier both advanced over the area and retreated from it since 5900 BC. That might mean it was warmer then than it is now, but not necessarily - the "recent" glaciation could have been caused by differences in climate other than temperature, like precipitation. Hypothetically, it could be that it has been warming since 5900 BC. Prior to that, the glacier could have existed but been relatively static at higher elevation. Warming would have caused some to melt, which changed the forces at play and caused the glacier to migrate down the slope. That would have allowed the vein to be accessible in 5900 BC, covered at some point thereafter by the movement of the glacier, then be accessible again today due to the glacier melting and/or continuing its movement to lower elevations. There's just not enough information in the article to say for sure, and I'm not familiar enough with the state of our knowledge of historical climate data to make an educated guess.