a qualitative scale in which minerals are classified in order of their increasing hardness, based on the fact that the harder of two materials will scratch the softer and will not be scratched by it. The scale lists 15 substances: talc (1); gypsum (2); calcite (3); fluorite (4); apatite (5); orthoclase, periclase (6); vitreous pure silica (7); quartz, stellite (8); topaz (9); garnet (10); tantalum carbide, fused zirconia (11); fused alumina (12); silicon carbide (13); boron carbide (14); diamond (15).Mohs scale.