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Dwarves' Earth Treasures Museum: How to ID Agate Roughs
Polyhedral Agates

-Typical colors: White, gray, black, colorless
-Typical sizes: Any sizes
-Typical shapes: Sharp geometric shapes with flat sides
-Most distinguishing characteristic: Geometric shaped nodules
-Special Notes:  Colors seem to be almost absent. A pair I have is only one I know of that has some colors (yellow, black, bluish-gray). Most nodules are quartz geodes.