Choosing a Crystal is a very personal process. And it is a very intuitive process as well.
If you want crystal for a specific purpose that you can directly take that crystals from anywhere such as from shop, on internet or from my store http://www.lifewithcolour.in, http://www.stores.ebay.in/life-with-colours
You can also pick up the crystal at random.
Trust you intuition.
Look out for one that ‘winks’ at you when in a shop or when browsing a net or directory.
There will no doubt be several to choose from. Handle several, allow yourself to be drawn to one, or put your hands into tub of crystals until one sticks to your fingers. If it makes you to tingle, it is the one for you.
Remember, that big or outwardly beautiful is not necessarily most powerful. Small, rough crystals can be extremely effective. Alternatively use a pendulum to dowse to help you to choose the crystal right for you.