The Rock Crystal is an item added by Astral Sorcery. It is used to craft Crystal tools and collect Liquid Starlight in Lightwells. It can be acquired by mining Rock Crystal Ore. Each Crystal has three stats: Size, Purity, and Cutting.
Size can be increased by leaving the Crystal in Liquid Starlight, and decreased by grinding on a Grindstone. Reducing a Crystal's size to 0 destroys it. Attempting to increase the size beyond the maximum has a 1/6 chance of splitting it into two crystals with random Size and Cutting, one with the same purity, and the other with 0-9% additional purity.
The effect of size depends on what the crystal is used for:
- The number of Lenses (but not PrismLenses) crafted
- The rate of starlight collection for Collector Crystals
- The durability of Crystal Tools
Purity can only be increased by splitting maximum-size crystals in Liquid Starlight. Purity provides a transmission efficiency multiplier to things that focus or redirect starlight; the multiplier is the square root of the purity (so 25% purity provides a 50% multiplier). The higher the purity, the lower amount of size that will be consumed out of a Rock Crystal or Crystal Tool when grinding them.
Cutting can be increased by grinding a Crystal on a Grindstone, which also reduces its size. Cutting affects the effectiveness of Crystal Tools and the collection rate of Collector Crystals.
Astral Tome entry