Well, there are so many books out there on crystals and their metaphysical effects. I thought I would give you my take on some of them.
The most evidence-based book is "Crystal Power, Crystal Healing" by Michael Gienger. Gienger wanted to circumvent all of the assumtions about stones that are made about stones, or channeled information.
So he gave stones to a bunch of folks who carefully journaled their responses to living with the stone. Then he compiled and compared all of their responses and reported the most common responses.
The first part of the book talks about the physical structure of the crystal families and the effects of the families. There are beautiful photographs of the limited number of stones that Gienger studied. Warning: some of the stones are out of alphabetical order--I don't know why. Perhaps spellings changed in translation from German.
"The Book Of Stones" by Simmons and Ahsian is a very extensive discussion of MANY stones by two of the most influential writers on stones. Both intuitives, they each give their take on any particular stone as well as some historical information.
This is a very useful book with lovely photos of each stone discussed. It is a heavy book, too heavy to lug to the store [I tried it, don't do it!], and has long discussions of each stone because each author gives his/her separate take on it.
It is useful for crystal healers, shamanic journeyers and folks who want to understand the uses of various crystals and stones including their uses in psychic development and healing.
"Love Is In The Earth" by Melody (updated version) is very useful and is found as a reference where most stones are sold.
There are NO PHOTOS. Instead there are Melody's intuitive assessments of an extensive number of stones plus numerologic associations.
Melody has lovely energy and her information is useful for psychic development, shamanic work, healing etc.
There are two books by Judy Hall that are reference compilations which I have found helpful:
"The Crystal Bible" and "Crystal Prescriptions" by Judy Hall.
"The Crystal Bible"" gives an unattributed abbreviated synopsis of various writers' opinions on crystals in a handbook format (5 1/2" X 6 1/2 ") which is small enough to carry to the store."
There are several color photos of most crystals in their various forms plus a brief chart of each stone with its color, appearance rarity and source (countries of origin). It is quite portable and is also often found where stones are sold as a reference.
"Crystal Prescriptions" is a handy index of symptoms/conditions/diseases/problems with useful crystals for each.
It also has an introduction section on the care, cleansing and uses of crystals, preparation of crystal essences, dowsing for correct crystals, chakras and associations, crystal layouts.
I would like to see this book better developed with more conditions included, but it is still extremely handy.
But the thing to remember about these books is that they can't replace your own intuitive response to stones. Reading about them is one thing, and living with a stone is another.
You will be amazed to actually feel some of the things described in the books and though they described it, they couldn't come close to actually imparting the true experience.
Other stones just won't resonate with you and you will feel little to nothing. Or you may have a negative experience that nobody mentions in the books.
I think it is all a matter of whether you resonate with a particular stone. The books are a great place to start and to get some idea of what they are used for, but experience is everything when it comes to your personal reaction to any crystal.
Best wishes in getting to know your friends,