The 4 C's - Carat, Colour, Clarity and Cut:

Information on the Carat of diamonds: https://www.diamondrocks.co.uk/magazine/diamond-carat/

Information on the Colour of diamonds: https://www.diamondrocks.co.uk/magazine/diamond-colour/

Information on the Clarity of diamonds: https://www.diamondrocks.co.uk/magazine/diamond-clarity/

Information on the Cut of diamonds: https://www.diamondrocks.co.uk/magazine/diamond-cut/

Glossary:

Carat: A unit of mass for weighing diamonds

Crystal: High quality glass

Zirconia: Diamond simulant / imitation

Lab grown / created diamonds: Chemically, physically and optically same as natural diamond, but origin is from a lab