A deep, glittering teardrop set in a solid silver closed bezel, hung on a 16 inch twisted silver chain.
Being upfront: the stone is green goldstone, which is a man-made glass rather than a natural mineral. It's made by melting glass with chromium oxide in a low-oxygen environment, which lets tiny metallic flecks crystallise inside the glass as it cools, that's where the sparkle comes from. 
It's been used in jewellery since at least 17th century Venice, sometimes under the name aventurine glass, though it's not related to the natural stone aventurine. 
None of that makes it less lovely, it just means you're getting a deliberately made material with a genuinely interesting backstory rather than a dug-up rock, and you should know that going in.
The bezel is closed (so the back of the stone is fully covered by silver, not visible like an open-back setting) and hand-set in solid 925 silver. 
Chain is a 16 inch twisted design, 1.5mm.
Materials and measurements:- 925 sterling silver, closed bezel, hand-set- Pendant approx 25mm x 18mm (estimated, let me know if you want this corrected to an exact measurement)- 16 inch twisted silver chain, 1.5mm
One-off piece, only one available.