These agates are called “black-skinned” because of their pitchblack outer shale. They were found in gravel-beds from rivers, that were running down from the Dekkan, a vulcanic highland in southern India. They were smoothed on the edges and sometimes very shiny polished by the transportation.
Occasionaly they are having a finelined grey-white banding. But they were highly searched after from collectors because this type of agate is very often containing awesome dendritic patterns.