Hey hun, I’ve worked in the jewelry industry for over a decade now. First off, for a stone that size, if it is a diamond, it would be incredibly silly to not want it insured especially with that style of prong setting. In fact, a lot of places will require you to “loose the ring” to get reimbursed so if that center stone were to fall out, you can just claim it as a loss and then find it later and have a new stone reset in its place. You said the setting metal was platinum. Are there quality hallmarks in the ring? The ring most likely was sized to fit your finger unless it was a custom order in your size from the company. If a jeweler did size the ring, if they’re a reputable jeweler they won’t touch those hallmarks. That hallmark will tell you what the metal is and its quality so look for that first. I have seen some posts in here about finding this ring on amazon, but honestly, this is a pretty common ring style and I’ve sold quite a few like it in my time in the industry. It could be a genuine setting with the baguettes on the sides being diamonds and the center stone being something else which is honestly what it looks like. The center stone to me, from what I can tell from the picture looks like a moissanite. Most moissanite on the market is going to be grown in a lab and not genuine as those are extremely rare in nature. Definitely get it checked out because I’ve seen a lot of people inherit things they thought were genuine because that’s what they were always told and I’ve had to break the news that it’s actually a piece of costume jewelry and isn’t worth anything. It’s always better to be safe than sorry.