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Use "octahedra" in a sentence
"Diamond crystallizes in the isometric (cubic) system, and regularly forms cubes and octahedra (an octahedra is an 8-sided "diamond-shaped" crystal; see below)."
"It crystallizes in octahedra, having a specific gravity of 3.2, and melts at 597° C. (T. Carnelley)."
"It crystallizes in red octahedra and dyes silk and wool yellow."