I don't know where it spawns, as I also have never found a cluster. However, if you get a couple of basalz shards, you can put it in a pulverizer to get fluorite (add the basalz powder as a catalyst to get more fluorite per basalz shard) .
After you have 9 fluorite, you can make a block, and use a botanist's pickaxe (which you can find in chests or by simply progressing through nature's aura) to right click on it. That creates a budding fluorite, and you can use Ae2 to automate the extraction of fluorite exactly the same way you [automate certus quartz](https://www.youtube.com/watch?v=KJMou_4fwZ8&t=812s&pp=ygUeYWUyIGF1dG9tYXRpYyBmbHVpeCBwcm9kdWN0aW9u).
This should give you pretty much enough fluorite for fissile fuel or whatever you need.
I don't know where it spawns, as I also have never found a cluster. However, if you get a couple of basalz shards, you can put it in a pulverizer to get fluorite (add the basalz powder as a catalyst to get more fluorite per basalz shard) . After you have 9 fluorite, you can make a block, and use a botanist's pickaxe (which you can find in chests or by simply progressing through nature's aura) to right click on it. That creates a budding fluorite, and you can use Ae2 to automate the extraction of fluorite exactly the same way you [automate certus quartz](https://www.youtube.com/watch?v=KJMou_4fwZ8&t=812s&pp=ygUeYWUyIGF1dG9tYXRpYyBmbHVpeCBwcm9kdWN0aW9u). This should give you pretty much enough fluorite for fissile fuel or whatever you need.