Halia Necklace with 925 Sterling Silver and Diamond Charm

The charm is stamped 925 and has a single diamond, tested and verified as a real diamond. The charm also has the brand name engraved in it. The charm opens up to function as a clasp for putting on and removing the necklace. It is approx 18" long. The chain itself is not stamped, only the charm, so I am unaware of its composition.