fortification agate

American  

noun

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

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Etymology

Origin of fortification agate

First recorded in 1880–85

Example Sentences

Its colors are delicately arranged in stripes or bands, or blended in clouds. µ The fortification agate, or Scotch pebble, the moss agate, the clouded agate, etc., are familiar varieties.

From Webster's Unabridged Dictionary by Webster, Noah

I found a piece of granite and a fragment of fortification agate in the sandy bed of the creek.

From Journal of an Overland Expedition in Australia : from Moreton Bay to Port Essington, a distance of upwards of 3000 miles, during the years 1844-1845 by Leichhardt, Ludwig