fortification agate

noun

an agate, used as a gem, having polygonal banding such that it suggests the plan of a bastion.

Origin of fortification agate

First recorded in 1880–85

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for fortification agate

Historical Examples of fortification agate

Sometimes they are arranged in angles, presenting the fortification-agate.
Scenes and Adventures in the Semi-Alpine Region of the Ozark Mountains of Missouri and Arkansas
Henry Rowe Schoolcraft