The Mohs Scale
The mohs scale was introduced in 1822 and it rates the hardness of gems and minerals. The scale was introduced by a German mineralogist, Friedrich Mohs. The scale is an assessment of how well a gem or mineral resists being scratched or abraded. Mohs put ten common minerals in the order with 1 being the softest and 10 the hardest. Basically, each gemstone can be scratched by the one above it, with diamond being the hardest.