please verify which adverb and adjective following sentences trying help my son and

Please verify which is the adverb and the adjective in the following sentences. Trying to help my son and I can’t remember. Diamond is a hard material. Hard is the adverb? Is there an adjective? Gems are stones used to make pretty jewelry. Pretty is the adjective? Used is the adverb? Gemstones are often found at the bottom of rivers. Often is the adverb? Is there an adjective?