gold is a chemical element (au from latin aurum) + atomic number 79. pure gold (24 karat) is soft, to make the metal workable it's mixed with silver, palladium, copper resulting in a variety of alloys, all precious matters jewelry are made with either :
23,5 karat (gold leaf) · 23,5 parts gold - 1 part copper, titanium or silver
18 karat · 18 parts gold - 6 parts copper, palladium or silver
14 karat · 14 parts gold - 10 parts copper, palladium or silver
to keep your gold items beautiful make sure to sleep, shower, swim, perform household chores, sport without them.
2,5 - 3 on the scale of mohs. glossy becomes a bit matte, matte becomes a bit glossy over time.