Vintage Sterling Silver And Moonstone? Brooch

I believe the stone is moonstone it reminds me of a cloudy sky in a way. It is really lovely. There is something on the very bottom of it like a speck I don’t know if it is in the stone or what please see above photo it is circled in red. Also the back has some kind of hard residue in one spot. But doesn’t affect wear or anything and it’s on the back also signed 925 Has wear but can be expected with vintage or antique items of any kind