Moissanite
A lab-grown stone that is harder and more fiery than cubic zirconia, and much cheaper than diamond.
Moissanite is silicon carbide. It occurs naturally only in meteorite traces, so every stone in jewellery is grown.
It is 9.25 on the Mohs scale against diamond's 10, so it resists scratching far better than cubic zirconia, which dulls within a few years.
It disperses light more strongly than diamond, which produces noticeably more rainbow flash. Some people love that; others find it reads as obviously not a diamond.
When you are buying
If you want a diamond substitute that will still look sharp in ten years, moissanite is the better buy over cubic zirconia and costs a fraction of diamond.
Cubic Zirconia
A hard, brilliant lab-made stone used as a diamond substitute. Called American diamond throughout the Indian trade.
Polki
An uncut, unfaceted natural diamond, set face-up in kundan. Glows softly rather than sparkling.
Gemstone
Any mineral or organic material cut for jewellery. Traditionally split into precious (diamond, ruby, sapphire, emerald) and semi-precious.
Karat
The purity of gold, measured in twenty-fourths. 24K is pure gold; 22K is 22 parts gold to 2 parts other metal.