The pendant might be dyed howlite, a common fake for real turquoise. The most distinguishing tests are destructive.
Hardness test: (THIS IS A DESTRUCTIVE TEST.) A steel knife blade will easily scratch howlite which has Mohs hardness value of 3.5 Turquoise has Mohs hardness of 5–6 BEWARE: Knife blade can still scratch turquoise. YOU HAVE BEEN WARNED.
Dye test: THIS IS ALSO DESTRUCTIVE TEST. If the pendant is dyed howlite, take some acetone or nail polish remover, and use a q-tip to apply it to the back of the pendant. If the q-tip picks up some blue color or exposed surface becomes dull or white, the piece is howlite. YOU HAVE BEEN WARNED.
There is only a slight difference specific gravity between howlite (2.53 to 2.59) and turquoise (2.6 to 2.9). Light weight cheaper quality turquoise may have the same specific gravity as howlite.
Best thing to do, take it to a lapidary shop or gem shop. A gem expert can tell howlite from turquoise by physically handling the piece and closely observing the color variations.