A Heartstone is a crystalline structure, or series of interconnected such structures, usually found deep within an aerolith. These crystals have a natural affinity for Silvermist, and draw the substance in continuously, amplifying its natural buoyant properties as it does so. As long as there is enough life and growth fueled by Silvermist living upon an aerolith, the Heartstone will keep its aerolith up in the sky.
When there is an overabundance of Silvermist for an extended period it can cause a Heartstone to grow, and eventually begin to raise the entire aerolith higher into the sky. But the higher up an aerolith is, the more power it takes to rise further, meaning that it is very hard to do this without a dedicated effort all across the aerolith.
Smoke interferes with the flow of Silvermist, as the two substances essentially annihilate each other on contact, so Smoke can literally choke off the power to a Heartstone, causing an entire aerolith to sink somewhat. As the aerolith drops to thicker mists, the power it takes to hold it up is reduced, and this usually allows a new stable altitude to be found very quickly – sometimes without anyone even noticing. All aeroliths rise and fall by small amounts over the years, with only the most catastrophic events causing a true fall from the sky.
The use of very small pieces of Heartstone crystal in an airship is being tested by at least one nation. If the idea works it may transform the entire field of airship construction and bring a new era of flight to Skai-Roon.