Well I will take a stab at this.It could be loadstone which does have magnetic properties and works on the same principle as the Shatki stone.Difference being ,it is a rock or rocks,cost a hell of a lot less and is more pure than the Shatki as it has not been immusilfied and mixed with glue. I use it on my transformers in my gear in little bags so that the dust and fragments from the rock does not enter the gear.My 2 cents.
Audiophile oddities
Since I changed my beloved YBA 2 preamp to a YBA 1 preamp, my 2 was lying on my work table. Yesterday I opened it up to see what was inside (a really beautifull inside...) but unlike the other time I opened it I went further in the body of the beast by opening those little black tinted box caled "YBA line module" ( I tought I would find some kind of esoteric electronic device...) and what I found was something I never imaginated I could find in a preamp: some kind of ziplock bag with some sort of black little rock (like those in fish aquarium) and absolutely NO ELECTRONIC PART!!! Just a plastic bag full of S**T. I tried to find if they where any electronic device under the board but again their was nothing. I will open up my 1 preamp to see if that is the same thing as the 2 but let me tell you that I'm a little bit disapointed that a profesional conpagny like YBA are using some kind of voodoo things...