Mystical Taurus Shard

ID#: 245386 Maximum Stack Size: 1 Recipe ID#: 553523 Recipe Cost: 9,999,999 999  Recipe Sold by: Adventurer Loric This item is created by Alchemy (20).

Mystical Taurus Shard Bound Requires Level 1 Tools Cannot be sold A fragment of an ancient, holy minotaur relic. It is still imbued with the mystical powers with which it was once suffused by the shamans. It can be used to grant greater powers to rings, earrings and necklaces of the mystic.  Recipe - Mystical Taurus Shard Requires Alchemy level 20 Raw Materials:  Spirit of the Ancestors ×1  Spirit of the Sun ×2  Spirit of Darkness ×3  Dust of the Altar ×9 Product(s):  Mystical Taurus Shard ×1

As with all Alchemy Recipes, the Crafting Cost represents the cost of the glassware plus any cost to use the Crafting Station (as displayed on the Crafting UI).

Very few Crafted items have no upgrade path, but this appears to be one of them.

The materials needed for this recipe are dropped by Trash and Bosses in Mystic Altar - Hard.

We are told that this item can be "used" to add a special enchantment to any of the Dark Accessories, Sun Accessories, or Ancestral Accessories dropped by Bosses in Mystic Altar - Hard. Other than that we have no specific information.

When using  Mystical Taurus Shard to upgrade the rarity of a Dark Accessories, Sun Accessories, or Ancestral Accessories, their durability, enhancement level, or Stats will not be modified. Players won’t need to worry that they will lose the enhancements and upgrades that are already on the Accessories. --from 5/7/2024 patch notes

According to Ainz on RoM Discord, Rare can become Epic, Epic can become Legendary. He also said that "50% chance that is went up, 50% chance that you'll get a blue item after that".

So,  Earring of the Astute Dark Mystic can become  Earring of the Astute Sun Mystic, which can become  Earring of the Astute Ancestral Mystic. The Stats and Durability remains the same. What changes is, you need 2 or 3 of the same Color and Naming to get the Set Bonuses.