"Prophecy Stone" - Hematite/Limonite Pseudomorph after Marcasite/Pyrite

These interesting pieces, referred to as Prophecy Stones, are a real oddity. Hematite and Limonite have pseudomorphed (crystallized and replaced) an earlier formation of Marcasite/Pyrite, keeping the original shape. 

From the White Desert, near Farafra Oasis, Egypt.

~1.5" x 1.5" - 71g