How many minerals are known to exist on the Moon?

Lots. A partial list of mineral types would include:

Plagioclase Feldspar
Olivine
Pyroxene
Silica-Quartz
Ilmenite
Potassium Feldspar
Chromite
Ulvospinel
Hercynite
Armalcolite
Troilite
Apatite
Whitlockite
Tranquillityite
Pyroxferroite
Chalcopyrite