The Collaborative International Dictionary
                    Calcedon
                    
                        
                
                                                                    Calcedon \Cal"ce*don\, n. [See Chalcedony.] A foul vein, like chalcedony, in some precious stones.
Wiktionary
                    calcedon
                    
                        
                
                                                                    n. A foul vein, like chalcedony, in some precious stones.