Mcguinnessite is a rare Mg-Cu carbonate, a member of Rosasite Group and is named after well-known California mineralogist, Al McGuinness. The matrix is richly covered with radial clusters and hemispheres of teal-blue McGuinnessite on most sides. Comes with an old Chuck Trantham label that indicates it was collected by Chuck and Al McGuinness in May 1982 and valued at $40 at that time.