Grossular Garnet, Ougrandite series.

Very gem-quality, beautiful color, perfect faces, very high brilliance.

Some very interesting clarifications thanks to Mr. Adrien Sautier: This is most likely a grossular pole. First, the layer of grey-green crystals suggests clinochlore, which would indicate a calcium-rich rather than aluminum-rich environment, thus ruling out the pyralspite series. If it is also a rodingitic fissure, the grossular nature is practically guaranteed. Another subtle clue: the faces of the trapezohedron appear to be modified not only by the (classic) dodecahedron, but also by the {321} hexactahedron. Now, in almost all cases, these forms have been observed on the ougrandite series.

Table credit: Pabst, A. 1943. Large and small garnets from Wrangell, Alaska. American Mineralogist, 28, 233-245