What’s in the Box? Shaping Up

You’ve known how to name 3D shapes since elementary school. They’re easy: cube. Cylinder. Pentagonal dodecahedron?

Pyrite - Pentagonal Dodecahedron

Crystal forms take on many fantastic shapes, and some have fantastic names to match. This pyrite from the Spruce Claim in Washington has twelve faces, and each face is a five-sided shape. A shape with twelve faces is called a dodecahedron, and the word pentagonal describes the shape of each face. Pyrite can also grow in cubes and other “closed” forms (meaning each face of the form is the same, like a pentagon, triangle, or square).

Dazzle your friends by pulling out the word scalenohedron at your next party. A scalenohedron is the proper term for the form “dogtooth spar” calcite takes, as seen here:

Calcite - Scalenohedron

This specimen is from Gallatin County in Montana.

Rice Northwest Museum of Rocks & Minerals
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