These so called “polyhedroid agates” from the state of Paraiba in Brazil are true rarities. After the 1970ies, when a bigger lot of this material hit the market, no more diggings were made at the finding location. Meanwhile good quality specimen are very rare.
Complete specimen af this agate-type are looking like beeing crystals or pseudomorphs after an unknown mineral. But they are telling the truth about their formation under the microscope. The outer rim of these agates is showing sometimes triangular striations. This is typical for the surface of tabular shaped calcite. So the agates should have been formed in the space between the calcite-crystals. Such formations are known as paramorphous formations.
These agates are showing usually greyish whitish and black tones. Yellow tones are rare.In Germany these agates are called “ Paraiba agates “, “ Polygonal Agates “ or “ Dreiecksachate “.