This chalcedony and quartzine plate is from Barros Cassal in Rio Grande do Sul, Brazil. These two minerals are silcates and contain the elements Si and O. Other trace elements can be incorporated into the crystal lattice causing a wide range of colors and morphology. This specimen consists of a plate of concentric, bullseye like, formations of chalcedony and its quartzine variety. These are formed by the dripping of mineral rich waters on a rock matrix which forms flattening stalagmites. They are also called conchas (Brazilian} for shell because they often resemble shells.The patterns or circles are created by the minerals growing at different rates.The patterns on the display side are covered with micro quartz crystals. It displays an attractive array of colors from red to blue. It measures 4 x 3 x 3/4 inches or 100 x 76 x 19 mm.