Mohs scale of mineral hardness
Geology   Wikipedia  
Talc(=1) Gypsum(=2) Calcite(=3) Fluorite(=4) Apatite(=5) Orthoclase(=6) Quartz(=7) Topaz(=8) Corundum(=9) Diamond(=10)

 Mnemonic:
Toronto Girls Can Flirt And Only Quit To Chase Dwarves .

 Mnemonic:
Terrible Giants Can Find Alligators Or Quaint Trolls Conveniently Digestible

 Mnemonic:
Tall Girls Can Fight And Other Queer Things Can Do!