The structure of the stones is shown in this illustration (please forgive the 'intergorth' typo:
The dumbbell structure including the central indialite crystal creates these intriguing stones which are not fossils:
The type locality is near Kyoto, Japan, of all perfect prefecture places. And these stones are found in a hornfels (metamorphosed shale or mudstone) matrix.
So much change in temperature and pressure in those metamorphic rocks to create these delicate hexagonal structures! The end result are muscovite replacement crystals of these cordeirite-indialite crystals all on the hornfels rock.
Chemically, indialite is a magnesium aluminosilicate mineral (Mg2Al4Si5O18). Cordierite is an iron magnesium aluminosilicate mineral ((Fe,Mg)2Al4Si5O18).
Have you heard of cherry blossom stones before? Does the complex interrelationship of the host rock, original crystal structure of two different minerals then replaced by another mineral in a hexagonal structure make you say "Wow?!"
New canine mountain friends on a perfect Colorado Day:
We said our Colorado au revoirs this weekend. . . ZOË is Addis Ababa bound, home-made injera sourdough flat bread in hand ;-). A most excellent adventure until September, 2017; Colorado peeps will miss you! Excited to hear about your grand adventure!