CREATE TABLE table_7697 ("Material" TEXT, "Formula" TEXT, "Refractive index ( es )  589.3nm" TEXT, "Hardness  (  Mohs' scale  ) " TEXT, "Density  ( g/cm 3  ) " TEXT, "State of the art" TEXT)

What hardness has a formula of y 3 al 5 o 12?
SELECT "Hardness ( Mohs' scale )" FROM table_7697 WHERE "Formula" = 'y 3 al 5 o 12'
SELECT "Hardness ( Mohs' scale )" FROM "table_7697" WHERE "Formula" = 'y 3 al 5 o 12'