Dendritic mineralisations in chalcedony. Dendritic (branchlike) precipitations of certain minerals are a well-known feature in geology. Most common are 'dendrites' of manganese and iron oxides that precipitate while water containing the dissolved minerals percolates along fractures and bedding planes in the rocks. The dendrites look like plant remains, but they are in fact entirely inorganic. Sample photographed in transient light, actual size is 63 x 80 mm.