In jewelry, S stands for silver, pt stands for platinum, pd stands for palladium, and G or 999 stands for gold. Platinum and gold are sometimes not pure gold, but k gold. Generally, 18k or 24k refers to gold content. K-gold is generally used to make rings inlaid with jewels, because pure gold is too soft, and K-gold is hard and easy to set. The so-called Una is either a brand abbreviation, if it is an abbreviation of metal materials. There is no difference between 99% and 925% silver. S925 sterling silver, which is very popular now, only refers to silver products with a silver content of 925%. The one with 99% silver content is not desirable, so I personally think this chain is hard to say. How long have you been carrying it? Is there any color change? If pure silver is easily oxidized, it will turn yellow and then black after wearing for a period of time. What you want to ask is platinum or platinum, which is essentially different, so please make sure that I am a student, not an expert ~ and don't listen to me, it may be really good money.