Insulation is about retaining heat.
In the netherlands there's been too much emphasis on heat retention in houses built over the last ~15 yrs or so -- these houses are uncomfortable during the summer, since retaining too much heat. Another interesting take is that "passive" houses require heaps of mechanical ventilation, and these systems wear out in ~15-20 yrs.
So over the course of the lifespan of a house, that adds up significantly.
Stone actually can work well with the proper detailing (dealing with cold bridging, styrofoam is a good way to break the cold bridging ):
Heat Storage: Stone, being a dense and heavy material, has a high thermal mass capacity. It can absorb and store a significant amount of heat during the day when exposed to sunlight or internal heat sources like heating systems. This stored heat is gradually released back into the indoor space during cooler periods, such as evenings or nights, helping to stabilize indoor temperatures and reduce heating or cooling requirements.
Temperature Regulation: The thermal mass of stone can act as a natural temperature regulator, slowing down temperature fluctuations within a building. During hot summer days, stone absorbs excess heat, keeping indoor spaces cooler. In colder weather, it releases stored heat, helping to maintain a more comfortable and consistent temperature.
Energy Efficiency: By using stone as a thermal mass material, buildings can reduce their reliance on mechanical heating and cooling systems. This, in turn, can lead to significant energy savings and lower utility bills, as the building naturally regulates its temperature with less energy input.
Passive Solar Design: Stone can be strategically placed in a building's design to maximize its exposure to sunlight during the day. This allows for efficient passive solar heating, where the stone absorbs solar energy and releases it slowly, reducing the need for active heating systems.