When quartz forms as a mass of microscopically small crystals it is known as 'microcrystalline quartz' or 'cryptocrystalline quartz'. This family includes all varieties of chalcedony such as agate, carnelian and sard. Opaque, granular microcrystalline quartz is known as jasper. Chalcedonies and jaspers occur in a huge variety of colours, created by small amounts of impurities such as iron, manganese and chrome.
The carnelian is carved with a late Roman intaglio of Hercules, signed in Greek 'Pela'.