Is this chain solid gold or plated?

It is 14k rose gold, so the color runs through the metal rather than sitting in a plating that wears off. That matters for a chain worn daily against skin.

Can it hold a pendant?

A small, light pendant is fine. At 1.25mm the chain is delicate, so a heavy or wide pendant will pull and stretch the links over time.

How does a spiga chain differ from a cable chain?

Spiga links are twisted into a tight braid, which gives a rope-like look and more resistance to kinking. Cable chains are simpler and cheaper but tangle more easily.

Will an 18-inch chain fit most people?

Yes, 18 inches is the most common necklace length and sits around the collarbone on most women. It layers well over a shorter chain or under a longer one.

How should I care for it?

Store it flat or hanging to avoid kinks, keep it away from perfume and chlorine, and wipe it with a soft cloth. Take it off before swimming or heavy exercise.