This is a dainty vintage art nouveau freshwater river pearl lavaliere pendant. 

The pearl is a natural tooth shape and has a white color with good luster. It is probably from the Mississippi river which was a large freshwater pearl producer at the time. 

It is made of solid yellow gold and features an art nouveau design. I measures 1 1/4 inch total. It is stamped "10K" on the bail and has a maker's mark. From the early 1900's.

All pearls are truly vintage and have only been lightly cleaned.