Which is basically HDPE (plastic) foil with limestone filler. And a whole website full of marketing that somehow never mentions that 20% of the material is non-renewable (made from petroleum products) and not biodegradable.

The premise is nice, but downsides noted in another comment, usability is also a problem.

It's much heavier than a normal notebook, and the surface is basically an extremely fine grit sandpaper. It works great with pencils and ballpoints, but wetter pens (gel, rollerball) do not dry as quick. Also, forget fountain pens. You'll be eating away your nib as I write on that paper.

I have a couple of these notebooks, but they sit unused for now.

Basalt is stronger than glass fibers (made from silica / quartz / sand), but not as strong as carbon fiber. Also, its more expensive than glass, but less expensive than carbon. Generally considered eco friendly.

Interestingly where carbon fiber's failure mode is instant, failing catastrophically (like say chalk), basalt will be more gradual (like say wood), in some use cases that's an advantage.

Overall though its still not mass produced, uncertain if it will ever reach scale.

If interested in fibers and composites, the YouTube channel Easy Composites is really interesting / educational. For example you can use flax fiber.

https://www.youtube.com/watch?v=AD98L9XlCTU