In 2 Corinthians 4:7, Paul says we have this treasure in jars made of what?

Answer: Clay

We have this treasure in jars of clay (KJV: earthen vessels) to show that the surpassingly great power is from God, not from us.

“Now we have this treasure in jars of clay to show that this surpassingly great power is from God and not from us.”— 2 Corinthians 4:7 (BSB)