Concrete

The heavy iron the earth makes — poured into foundations, and it points north.

Magnetite · The Law of Power

Family: Iron oxide — Fe₃O₄
Hardness: 5.5–6.5 on the Mohs scale
Colour: Iron black with metallic lustre
Signature: Naturally magnetic; used as heavy aggregate in real concrete

The stone read as the word

Magnetite is one of very few minerals that is magnetic straight out of the ground; lodestone was the first compass. It is also poured into high-density concrete when a structure has to be heavy enough to hold and to shield.

So it is literally both things this word means: something solid enough to build a foundation from, and something that keeps true north while it sets.

What it is carried for

Carried before she puts her name to anything.
Held so endorsement waits until the ensuring is finished.