I bought a beautiful, gold, herringbone necklace.

Herringbone is a type of fabric cloth. It has a distinctive type of weaved pattern and it achieves its name because it has similarities to the pattern of a herringbone fish.

I believe you are referring to a "herringbone stitch." Here is a video link showing how to make a herringbone stitch:

http://www.wonderhowto.com/how-to-herringbone-stitch-191551/

Herringbone isn't a fibre - it's a weave pattern. Could be made from natural, or synthetic fibres.

Herringbone. Dogtooth