I often use the term CGDOT (Cute Girls Doing One Thing) to describe that subgenre of CGDCT that specifially centers around a certain gimmick. I think it's actually more common than the original idea behind the genre of showing the little wonders of life through the prism of le moe anime girls that both do many things and ultimately nothing at all.

Just think about it: you want to write a manga, preferably for long enough so your parents dont tell you to go find a salaryman job any time soon, but all you've known all your life are anime girls and one hyperfixation that came bundled with autism. Combining the two together gives a result that you can yap about for at least a hundred chapters, be reasonably successful and enjoy making something moderately good.

a few examples:
/anime/14355/yama-no-susume (girls hiking)
/anime/109019/houkago-teibou-nisshi (girls fishing)
/anime/104679/rifle-is-beautiful (girls shooting)
/anime/113418/super-cub (girls on bikes)

It's a much easier thing to make than a story about characters doing absolutely nothing special, or very episodically so. But it is done at the cost of being niche, often being too specific for a wide audience, and usually lacking the soul and spirit of the superior CGDCT genre.

Ruri Rocks manages to be above most of these, but while still having the gimmick as its centerpiece. It's especially a feat given how geology is usually seen as a lower science, being especially boring. The anime manages to make it both very enjoyable and very approachable, which is something the genre criminally lacks. It's very rare in these times of sloppy, soulless productions to feel you've actually learned something from the 24 minutes you just watched, especially in every episode!

In a sense, I'd say Ruri Rocks is closer to /anime/151514/chi-chikyuu-no-undou-ni-tsuite ///anime/329/planetes for how packed with information it is.
What's best about it is it has the exact same structure as all the other shows I mentioned, new girl who's not interested in a topic discovers a new hobby and meets with new friends. However it is simply done better, it do be like that sometimes.

The production is also great, Studio Bind may be young and make questionable productions but there's no denying they know how to design characters and proper color harmony. It's also something most CGDOT dont excel in, the topic isnt often put in the center, whereas here every scene showing a new kind of shiny rock is a money shot.

Ruri Rocks is above the rest because not only is the material good, but the adaptation was done with the right vision in mind. The manga panels have a charming style but it's not good enough to give the reader the full measure of how beautiful minerals can be, the studio managed to understand it and show just what can be so fascinating about the shiny rocks.

Usually people come from the gimmick and stay for the girls/the sunken cost fallacy but here, the topic manages to be the best part of it all, well of course it's also packed with a good amount of suggestive camera shots that cater to the whole gooner spectrum, but it's not the main appeal for once.

And btw: