Andradite

Formula: Ca3Fe3+2(SiO4)3

Andradite is relatively rare, but is the most abundant of the Garnet Group minerals. It occurs in miarolitic cavities in nepheline syenite, in marble xenoliths, and associated skarn contact zones. Crystals are generally rhombic dodecahedrons, with colours ranging from yellowish-green to dark olive-green. Yellow octahedral crystals such as those below, were found in marble xenoliths.

Yellow crystals of andradite. Width of view 1.53mm. Doug Merson specimen and photo.
Green crystals of andradite. Width of view 3.49mm. Doug Merson specimen and photo.