Chalcedony

Chalcedony

Chalcedony,  SiO2   is a cryptocrystalline mineral formed from the intergrowth of two silica minerals, Quartz and Moganite.  The specimen, from Normandy in France is in the form of part of a geode. The outer wall of the geode exhibits the conchoidal fracture associated with Quartz. and the interior is lined with mammarian growths, of a pinkish hue, which are soapy to the touch.