Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/360

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Primitive crystal—an octahedron composed of two obtuse quadrangular pyramids joined at their bases, which are square.

Fracture—mostly shattery, often vitreous; sometimes conchoidal, sometimes lamellar.

Aspect—non metallic.

Hardness—brittle and easily frangible; gives sparks with a steel.