9mm. Van Cleef & Arpels red chalcedony necklace is divided into three sizes, namely small, medium and large. The small 9mm is suitable for stacking, and the medium size of 15mm is very effective, and many people like it. Van Clive &; Arpels) is a French luxury brand, which belongs to Richemont Group. Van Cleef & Arpels mainly deals in jewelry, watches, perfumes and other products.