The seventh and final chakra is the crown chakra, represented by the color violet. It is sometimes also represented by white.
This chakra controls wisdom and true understanding. When the seventh chakra is healthy, it allows you to plan your life and handle the daily trials and tribulations that life throws at you. You will feel your link with the Divine and with the rest of creation.
When your seventh chakra is unhealthy, it leads to unwise decisions, unhappiness, and a sense of indecision. You will feel alone and seperate.
If your aim is to open your seventh chakra, then you should start with amethyst or quartz. Meditation is a key to developing the crown chakra. Visualise a beautiful flower at your crown with hundreds of petals gently opening. This will help you find wisdom and a sense of universal connection.
If the problem is that your seventh chakra is too open, and you are finding it hard to cope with the hustle and bustle of everday living then imagine the same flower gently closing the petals over to protect the chakra.
For a really indepth chakra read go for Cyndi Dale's
The Seven Chakras