A mantel is the shelf above a fireplace — also written mantelpiece. A mantle is a cloak, and figuratively a role or responsibility passed from one person to another: take up the mantle. The Earth's mantle uses the second spelling too.
The core difference
A shelf and a cloak, historically the same word.
- mantel — the shelf above a fireplace: photographs on the mantel.
- mantle — a cloak; a role inherited: assumed the mantle of leadership. Also the Earth's middle layer.
The connection
Both come from Latin mantellum, cloak. The fireplace sense came from a hood or covering over the hearth — a cloak for the fire — and the spelling later split to separate the architectural feature from everything else.
The figurative use
"Take up the mantle" comes from the idea of inheriting someone's cloak and with it their authority — an image with biblical roots in Elijah passing his mantle to Elisha. It is always mantle, never mantel.