If staining is very heavy or you want to speed the process along you can heat the solution by standing the bucket in the hot sun. There are some who use an old crock pot instead of a plastic bucket, and heat their acid solution that way. Be sure not to do this indoors because of the toxic fumes the acid puts off. Do not use any type of metal or aluminum container for the acid will create a toxic gas cloud, please remember to use rubber glove and a mask at all times.
When the crystals are clean to your satisfaction, rinse and rinse them again. If you have hard water in your area, it is smart to use distilled water for rinsing to prevent possible yellow staining of the crystals. Soak them in clean water for a day and then allow to dry.
** If the crystals develop a powdery coating as they dry, soak them in a baking soda solution of about 1/3 cup to a gallon of water then rinse well.
Another method for removing iron stains is Naval Jelly, which contains phosphoric acid and is sold for getting rust off of metal, but will work on quartz crystals also.