Chalcedony. A semi-precious gemstone named after the close by town of Chalcedon, and is sold in most of Istanbul's multitude of jewellery retailers. Shopping for an Istanbulkart is a good suggestion if you are in Istanbul for in excess of a day or two, and plan to use community transportation. https://istanbulwordpress72738.blogdun.com/37702986/istanbul-personal-portfolio-wordpress-theme-for-dummies