Instead of using Rock Crystals you can use Celestial Crystals. Throwing a single Stardust and a Single Crystal (attuned/un-attuned Rock Crystals or even Celestial Crystals to re-roll their stats) into Liquid Starlight and waiting will turn them into Celestial Crystal Clusters.
These Crystal Clusters need to be left to grow, so do not harvest these straight away. You will know when they are matured and ready to harvest when they have small white particles coming off of them. Other methods of detecting whether or not a Crystal Cluster is ready for harvest is to check it’s metadata in the F3 menu (or if you have a mod like WAWLA or TheOneProbe installed and configured correctly). A Crystal Cluster with a metadata of 4 means it is fully grown and ready for harvest. When harvesting (with an iron pickaxe or above) you have a chance to get Stardust back.
You can increase the growth rate of Crystals by directing Starlight (e.g. from a Collector Crystal) towards the cluster. In addition, breaking a fully grown Celestial Cluster on top of Starmetal ore has a chance of yielding an extra Celestial Crystal. However, the cluster will continuously revert Starmetal ore back to iron ore, so it is recommended to also have the Collector Crystal link to the iron ore as well.
Celestial Crystals are stronger and bigger in size compared to their “Rock” counterparts (900 as compared to 400). The Size, Purity and Cutting of these Crystals are random. Even if you spawn in a 400/100/100 Rock Crystal, it will never be a perfect Celestial Crystal. In almost all cases in vanilla Astral Sorcery (with no modpack specific configurations), Celestial Crystals are equal to or strictly superior in any situation where a Rock Crystal can be used (unless it’s crafting something which does not care about Crystal stats).