Have the shamans prepare a sacred fire, and place the somewhat dim thunder-rock at its centre. Observe, leaving the stone in place until the flames die down.
(4)The fire-light takes some time to build, as you need to create one large enough for the ritual you have planned and safe enough that the fire won't spread to the surrounding plants. You build it just outside the cave, on a flat area that only needed the plants already there to be cut back and removed for fibre or food uses. Soon enough you have a pyre as wide and tall as a fang-beast, host to a roaring fire-light very much suitable for your purposes. You are given the honour of placing the thunder rock at the centre of the fire and, for a moment, it seems as though nothing is going to happen.
Then the fire roars far above the normal height of such a fire, seemingly leaning away from the thunder-rock at it's centre! A horrendous crackling noise fills your ears as the fire bursts out in every direction away from the thunder-rock, almost scorching some of your shamans before they move away from the fire! Luckily you planned in advance, and the surrounding area is clear enough that nothing else begins to burn, but the crackling and height of the fire prove incredibly intimidating. You and your shamans watch in awe as the fire continues to rise, higher and higher into the sky, only to suddenly fizzle out as the entire fire simply... stops existing. After staring with some confusion at the pile of sticks where there was once a fire, you are the first to step forward and slowly reach for the rock, only to leap backwards as the finger you poke it with burns.
Eventually you try to pick it up again and, while it is uncomfortably warm to touch, you are at least able to pick it up. Though, you must say, it doesn't seem much brighter - if anything you're now pretty confident that it has been dimming. It's gone from being quite shiny when it was first discovered to having a bright glow, but it doesn't really shine as much as it used to. When you put it through the usual tests over the course of the next two moon-turns, you find that it's response to touch seems to actually be weaker than it was before the fire! You're pretty confident this means that the thunder-rock spirits and the fire-spirits don't like each other. Perhaps it is because they are both powerful, active forces which dislike being unable to deal with something? Your shamans confirm that fire spirits and rock-spirits have a natural dislike of each other, so you suppose that must be the case.
Spring has turned to summer as there have been two more moon-turns and the great spirits of prosperity have turned towards the great spirits of heat for guidance in fighting the ever growing power of the great spirits of cold.
What are you going to do? There are no issues of immediate importance, but I would like to remind you that time will pass quicker in game if more of you post actions. Updates will also be larger if you do that, generally speaking.