Citrine

Citrines, like these shown here, and topazes are sometimes misidentified. If you have a piece of rough yellow stone that's scratched by an 8 but not by a 7, you've eliminated topaz (hardness 8) as a possibility. Stones of the same hardness won't scratch each other. As yellow quartz, citrines have a hardness of 7. Photo by Mauro Cateb. Licensed under CC By 2.0.

Article: Destructive Gemstone Tests: Scratch Testing

Credit: Mauro Cateb