What is a natural resource that is plentiful, but strong enough to be used as currency?

The two characteristics - "plentiful" and "currency" - are not really related.

Money is a symbolic tool to expedite trade. In earliest days, people might carry bushels of wheat to exchange for jars of oil. But that is cumbersome, and the search costs are too high. It's hard to find another party who both wants what you have, AND who also has what you want!.

Instead, we all agree on trading with "money." The farmer gives the store milk and gets money. Later you give the store money and get milk.

SO ... The most important characteristic of currency is that it is hard to fake. That is to prevent cheating. Gold and silver were scarce so made good coins. Then printed currency was made hard to counterfeit. Trade with money is based on confidence in the money.

In an entirely different direction are the natural resources we take for granted - like air and water.

If you explain your question further in the comments, glad to respond.

Explanation:

Nature.

Real value equals nature which sustains all life.

This is indisputable & real value, nature & life are inseparable.

Nature is a singular compound billions years old recreative self-sustainable real value system of living organisms. Humans are a mere millions years old failing species of mammal.

Nature must and will inevitably be repaired, restored and expanded as the only source of REAL life sustaining value on the planet.

Value inequality concerns natures real life sustaining value and over billions of years through evolution nature has acheived some degree of balance. This has been disrupted by the human species using the failed fake value system of economics to create fake income inequality

Real value is not * emotional * or * symbolic * (wealth) and for mammals like we humans consists of life sustaining matter created solely by nature.

Fake "value" or wealth is created by failed economics which creates fake income inequality that is used to manipulate the masses access to real value. Fake value is "shadow wealth" used by capitalists to control and manipulate access to natures real value.

Wealth is a fake value lien placed by the wealthy (capitalists) on natures real life sustaining value and is facilitated by economics and capitalism in particular.