Quartz crystal - Overall balance of the chakra system. Amethyst - Aids understanding knowledge, calm and mental organising. Sodalite - Communication, personal expression and the flow of information. Green quartz - Deals with relationships and personal development. Citrine - Helps give self confidence and personal power. Agate - Its functions are creativity feelings and sexual drive. Hematite - It gives stability energy distribution and physical survival.
We say: These crystals can be placed on the body following the above guidelines, or by using your intuition if it directs you otherwise. For example, maybe your intuition guides you to use amethyst on your heart chakra and green quartz on your third eye. There are no right or wrong ways to use the chakra crystals and chances are if you feel "guided" to use a certain crystal on a certain point, it is most likely to be the most beneficial point to place it.
Don't forget to regularly charge and cleanse your crystals. Cleansing can be as simple as running the crystal under the cold tap while visualising the negativity being washed away. A night on your windowsill in the moonlight (full moon is particularly effective) will give your crystal an energy boost. Sunlight works just as well, but some crystals may fade.