#cherry-blossom

They have a complicated origin. These rocks started out as shales – sedimentary rocks, probably deposited on the floor of an ancient ocean. As Japan grew, those shales were compressed and heated near magma chambers from the Japanese volcanic arc. That heat caused two chemical types of the mineral cordierite to form – the first crystal of cordierite formed and then 6 different cordierite crystals grew, radiating around the core. After those minerals formed, the rock sat there for a while and cooled off, but it was later reheated by another magmatic system. This time, the magma didn’t just add heat, it also added water from magmatic, hydrothermal fluids. Those fluids reacted with the cordierite and converted it into muscovite – a much shinier, if more friable, mineral. These rocks break easily but as you can tell they’re both fairly nice collectors items and quite rare due to the complicated sequence required to form them. -JBB Image credit: James St. John https://flic.kr/p/p1idTH Read more: http://www.mindat.org/min-1128.html https://www.wordnik.com/words/subhexagonal http://bit.ly/1LMffEU