The agate in these thundereggs have blueish, white or just grey colours, rarely with some orange. The green cavities wall mineralization is Seladonite (Zwickau is the type locality for this mineral). In many eggs more than one generation calcite psuedomorphoses can be found (mostly quartz after calcite I believe), sometimes also radial patterned, white – greenish – purpleish fluorite bunches.
Very distinctive are the xenolites, the inclusions in the shell. A xenolite often is the nucleation point of the egg; in the Planitz eggs they have various shape and color.