Left: metal/gold 金 (Covered in the ground 土 are 2 gold nuggets 丷), right: "not good" 艮 ('good' would be 良, but the accent 丶 is missing, thus 'not good')
Mnemonic
(Gold would be better!) This metal is 'not good', it is only silver.
The app has many other functions, such as character selection according to difficulty, practice programs, handwriting recognition and success statistics!