Approximately 11mm or slightly less. This is top-quality material, packed with lepidocrocite and goethite, resulting in a vibrant red color. Perfect for your handmade projects! Get 50 yen off for every 2 items purchased, so please take advantage of this offer! ♡ To avoid any issues: Please be aware that natural stones may have natural cracks, scratches, chips, and inclusions ◡̈⃝︎⋆︎* There may be a slight size difference of approximately ±0.5mm, so the size is listed as approximately ○mm. These are not perfect like artificial glass, so please understand before purchasing ◡̈⃝︎⋆︎*