From: Dictionary of American Naval Fighting Ships, Vol. IV p 433

Moonstone

A transparent or translucent feldspar of pearly or opaline luster which is used as a gem.

Moonstone (PYc--9), formerly Lone Star, was built in 1929 by Germania Werft, Kiel, Germany ; acquired through purchase from Frederick H. Prince, Aiken, S.C., 10 February 1941 ; converted by Gibbs Gas Engine Co.. Jacksonville, Fla, ; and commissioned 10 April 1941.

On 2 May 1941 Moonstone sailed for patrol duty with the Panamanian Sea Frontier until 2 January 1943, when she sailed for Ecuador to aid in training that country's navy. In March she sailed to Charleston, S.C., to prepare for permanent transfer to Ecuador, and in July returned to Panama, where the transfer was to take place. Upon arriving Balboa, however, cracks in the cylinder blocks of her engine were discovered, and she was ordered north for repairs. On 16 October in the south entrance channel off the Delaware Capes, she collided with Greer and sank immediately, losing one of her crew.