The center stone measures 25 x15mm and is a genuine agate (of some sort). It's also a tiny bit loose in the setting (you can hear it jiggle when you shake it). It is not stamped sterling silver but appears to be silver. Size 6 Please inspect and enlarge the pictures to assess the condition of the item for yourself. Please ask any questions you might have. Vintage/Pre-owned/antique items are being sold as is. Pictures are not altered and colors have not been adjusted. Due to technical reasons, colors may appear differently on your electronic devices. Pictures may also be enlarged to show better detail. 💎gemstone, 14k, 10k, 18k, sterling, silver, gold, estate, ring, pendant, earrings, loose, natural, stone, genuine, synthetic, lab, diamond, moissanite, vintage, real, gemstone jewelry, engagement, anniversary, promise, wedding, plated, gem, necklace, brooch, fire, crystal, jewel, gift, authentic, collectable, affordable, tested, luxury, natural, opal, emerald, aquamarine, topaz, sapphire, tourmaline, zircon, spinel, investment, ruby, alexandrite, stamped, investment 💎