This chalcedony and quartzine plate is from Barros Casal in Rio Grande do Sul, Brazil. Chaledony and quartz are silicates containing the elements Si and O. Other trace elements can be incorporated into the crystal lattice causing a wide range of colors and crystal morphology. This specimen, often called a concha ( Brazilian for shell), consists of a plate of concentric, bullseye, like formations of chalcedony and its quartzine variety. This piece is curved with a clam-like appearance. It was formed by the dripping mineral rich waters forming flattened stalagmite-like formations that assume the shape of the matrix that they grow on. The patterns on the display side are created by the minerals growing at different rates. The rear is the former attachment point and it displays a different texture and growth pattern. The display side is attractive with its array of blues and greys. It measures 1 1/2 x 1 3/16 x 7/16 inches or 38 x 33 x 11mm.