*best don't combine a precious stone with a semi-precious stone because the energy of a precious one is to big/strong and the other ones aren't effective anymore...the precious overwhelmes the aura of the semi-precious, precious ones are for example ruby, sapphire, smaragd...
*the other thing i know is that you have to look at the color-combinations...some stones have a totally different energy than another and could work against eachother...colors that don't fit together work mostly not good together...that's a basic rule...but i myself don't know much about this...
*clear cristal/rock cristal: this stone is good with all stones, it can't be bad, it strengtens the power of the other stone...
i would say just look up the meanings/qualities from the specific stones and compare them...are there qualities who work together, are the same or are there some opposites??? if there are opposites...then maybe one of the stones don't fit with the others or maybe, only one is the best for the purpose...
amethist is definatly good next to your bed but i don't know about the other two...
! a good tool to use is a pendulum to know what is good for you...what fits together and not but i never tried...but with a pendulum you can even search wich color from a certain stone is the best for you for example smoky quartz: you have diffenrent colors in it: you have light and dark ones...with a pendulum you can pick the color who best suits you...
btw: what is a blue john *shame on me*???
a site i use sometimes is this one...
http://www.mahatma.co.uk/crystal_manual/crystals/
http://www.mahatma.co.uk/crystal_manual/contents.htm
http://www.rainbowcrystal.com/crystal/stonecat.html
i hope i have helped you a bit, hum...i don't know af any sites who go about combining...have you looked it up with google?
with much of love,
sara