Pool spar are simply well-defined crystals that grow underwater in cave pools, and are a subtype of spar crystal. Usually, they are composed of calcite. Often the pool in which the crystals grew has evaporated or fills only seasonally. Pool spar is often found on the bottom of shelfstone. Pool spar may also coat the end of a stalactite that extends into a pool that has inundated it, in which case it is called a bottlebrush, which has a separate page here.
Most pool spar is of the “dogtooth” variety, coming to a point as shown in the top photo. But other pool spar, especially that formed along the flat surface of the pool, may form in a triangular shape, as in the middle image.
AUTHOR: Dave Bunnell