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 Project Gutenberg

The varying manner in which these materials are arranged causes the agate when polished to assume some characteristic appearances, and thus certain varieties are distinguished, as the ribbon agate, the fortification agate, the zone agate, the star agate, the moss agate, the clouded agate, &c.

From Project Gutenberg

When the deposits in an agate have been formed on a crop of crystals, or on a rugose base, the cross-section presents a zigzag pattern, rather like the plan of a fortress with salient and retiring angles, whence the stone is termed fortification agate.

From Project Gutenberg

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

From Project Gutenberg