I would classify gold as an underground treasure, high in value that can be issued with sentimental value.
Or in smaller kid langue...
I would classify gold as an underground metal that can be used on jewelry or to make something that could mean something to someone.
If your in 2-4, I would use the second one. If you are in a grade higher than 4th, go ahead and blow your teachers mind by writing the first one. PLEASE do not copy it word for word! Make it your own so you do not plagiarise!
Plagiarise- "copy from {someone} and pass it off as one's own." (google web)
