those Lisa are a tumbled and polished stone usually for stone therapy and they wont get as hot as if you were to want to heat stone for water to keep it hot...those for water would be heated to a higher temperature needless to say...

if your back and shoulders are getting sore...may i ask what sort of stones your using for them when you heat...and may i also make a recommendation as to the sort you would/could use...???

for instance to stimulate blood flow to a area you would use red or orange such as orange in citrine or red as in blood stone...blue/green stones help to calm inflamation such as azurite...for pain a very good stone is flourite which comes with rainbow like colors in one stone very pretty and really works...thing is with it..it works so well after awhile you will see fractures within the stone itself as it does this and when you do then its time for a new stone...

hematite has legs...seems to like to wander on you but a very excellent calming/grounding stone when your getting frazzled giggle..

blue/green is also good for the throat...facinating about crystals isnt it...

and here is another one to usually have on hand is a double terminated clear quartz crystal meaning pointed at both ends and always try to get one with at least 6 sides to the pyramid like ends/just make sure the tips are not broke off...this evens out energy within a certain area to help with the pulses of electricity within our bodies that we carry...and get the flow of energy going again in both directions when it gets blocked.

i did a lot of studying with a native american medicine man(men) about this sort of healing energy...being native myself and a active member of a intertribal council ...i had a lot of opportunities to learn a lot of things...from a few nationally and internationally traveled mentors in the native medicine fields...

enjoy your ***crystals and always keep them cleansed after each use...