Empty Crystal空の水晶

A rhombus-shaped crystal made from glass that has complex circuits embedded. It seems powered down, maybe it could be fed data to activate it again?
In-game description

How to use Empty Crystal

Empty Crystal is used to craft Admin Key. You do not need a crafting station: you use Empty Crystal itself.

Have the materials in your inventory (Shutdown Protocol ×1, Anomaly Report ×1, Overwrite Transcript ×1).
Put Empty Crystal in your hotbar, select it and use it (right-click).
Admin Key is crafted.

Empty Crystal key points (from the game data)

Sells to merchants for 600 Ancient Coins.

Calculated and summarized by this site from the game data (1.3.0.6).

What is Empty Crystal used to make? Craftable items and their uses

Items you can make with Empty Crystal, with how to craft them, the other materials needed and what the result is for.

Admin Key

How to craft: Hold Empty Crystal and use it (no crafting station needed)
Materials: Shutdown Protocol ×1, Anomaly Report ×1, Overwrite Transcript ×1
What it is: Admin Key is the key that opens the door in Glyph Parchment Treasury.

The game data has no recipe or source for this item.