Very odd druse crystals (SiO2) on what appears to be something that was once organic or calcified -- wood or coral. It's a piece from a larger formation. Very attractive.
Druzzy quartz bordering on chalcedony from a hydrothermal pocket. Got the first part Tiger The rougher vugs may have had another mineral that has since eroded out~ possibly a carbonate~ that would have been a base rock that the quartz began forming on.