I was starting to assemble the  section about specialized formations of quartz crystal
and was going over some crystal properties when I had one of those Whoa! moments.
Yes those formations work and the properties of stones  listed in books will often be just right  for your needs.   On the other hand you need not  strain to find a particular stone or formation.  It is far more important  to learn to pay attention to, learn to recognize and to trust your intuition and inner guidance.
If you need a particular stone or crystal formation  then the universe will help you find it.
You will either find that stone or you may already have it . It may be hiding in your collection until the right time or it may connect with you by attracting you at a store.
 A bird may drop it at your feet!  I have a raven gifted pebble.

There are a lot of different specialized formations of quartz highly advocated for particular purposes and there are huge lists and volumes about what each kind of stone is used for orcan do. This information can be a valuable resource and many times the information you find in these books will be just what you need to know , Other times you might be better off throwing out all the books and just grabbing for the nearest rock.

Sometimes crystal that has the effect you want will also have one you don't want. For example people often work with amethyst for dream work and to open higher self connection. Some people who are also dealing with depression or nervousness may find that  amethyst makes those conditions feel worse because it can  brings them to the surface.
 This is not a bad thing  you may need to be aware of a condition to heal it but it can be disconcerting if you were intending to work in anaother way or on a different issue.

When we have a specific need or purpose in mind and do not know what stone to use It is quite common to start searching for the right stone by pulling out a bunch of crystal books or gemstone properties lists or doing a web search to find a stone that is traditionally used for what we want to do.  Often however the best stone for you won't be on that list or it
won't really be the right  stone for you .

Everyone is different and even though one stone may come highly recommended for particular work it may not be the one that will help you. Learn to develop a connection with spirit and trust both your intuition and inner guidance.  Some people feel a vibration in their hands or heat or see light or hear a sound when they have their hand over the right crystal for the particular need.

If I know that I need a stone for a purpose and none of the ones I have call out to me,  I sometimes use the crystal books like a divination tool letting the book open wherever it wants and using a coin or pin or finger to pinpoint the line in the book to read It will often point you to just what you need. 

There are several different decks of crystal cards  which can also help one select stones.Shuffle the deck and pull out a card  when it feels right.  Some people use a pendulum held over the stones they have to help select the right stones.
If you have an assortment of crystals That you can put in front of you and you can look at them and meditate asking to know what to use for your purpose and choose the ones that seem to attract or call you.

When you have a clear and focused idea and intention for what effect you need You will attract the means of achieving that effect into your life be it a stone or energy or something else. One time I was looking for a stone to ease my aching feet and I attracted a  free foot massage.

You can also go into meditation and ask your high self , Solar angel, Spirit guides and or the actual stone deva to connect you with the stones and or energies that you need for the purpose.   There are attunements in the Crystal Deva empowerments which help remove obstacles and help devlelop the intuitive connection with  the Crystal Deva. 
Once you have some familiarity with crystal healing You are likely to find your intuition and intuitive guidance kicking in Follow that. Trust the stones  and the Crystal spirit /Deva.