It is certainly not a sin to wear jewelry if worn in moderation and in a wholesome manner.
In Malachi 3:17, God even compares His children to jewels. He would not do this if wearing jewels were inherently sinful.
However, other scriptures show us that, along with some other forms of personal dress and grooming, if jewelry is used improperly or in excess—that is, in an immoral or vain manner—then it is frowned upon by God. Please see Isaiah 3:16-24; Ezekiel 16:17, 39; 23:26; Hosea 2:13; I Timothy 2:9-10; I Peter 3:1-3.
Clearly, the attitude and motive of the wearer are the important factors in adorning oneself with jewelry. Of the proper attitude, Peter writes, "Let it be the hidden person of the heart, with the incorruptible beauty of a gentle and quiet spirit, which is very precious in the sight of God" (II Peter 3:4).