01. Durable
Gold does not rust, tarnish, or decay under normal conditions.
Economics & History
Gold is not particularly useful. You cannot eat it, build with it, or make weapons from it. So why has every civilization agreed it is priceless? An alien economist would find a soft yellow metal with niche industrial uses and then discover humanity has treated it as wealth for 6,000 years. The alien would want an explanation. Gold conquered economies because of chemistry, psychology, and physical properties that make it uniquely suited to money.
Quick answer
Gold became associated with wealth because it is durable, rare but available, divisible, portable, recognizable, and hard to counterfeit with pre-industrial tools. Out of all elements, gold is close to the only one that passes the monetary Goldilocks test.

The mystery
Gold conquered economies because of chemistry, psychology, and physical properties that make it uniquely suited to money.
The short answer
Gold became associated with wealth because it is durable, rare but available, divisible, portable, recognizable, and hard to counterfeit with pre-industrial tools.
The twist
Out of all elements, gold is close to the only one that passes the monetary Goldilocks test.
Common mistake
Gold's value is often described as purely conventional.