What defines a 'quarry' in Civ 5?

Solution 1:

A Quarry is a tile improvement constructed by Workers on Stone and Marble resources. It requires the Masonry tech to build. Stone Circles does not benefit resources requiring Mines to improve like salt, iron, or gems.

Solution 2:

Quarries are only for Marble and Stone. Salt and Gems use mines, as do other metals like Iron and Copper.

Solution 3:

Whenever I'm playing and am not sure on what kind of improvement can be placed on a resource (Plantation, Quarry, Mine) You can go to the HELP and type the name of the resource. This will tell you what improvement will be placed on top. You can do this before founding a Pantheon or even enhancing your Religion so don't blow your choice.