Harvia Rounded Sauna Heater Stones Olivine Diabase (2-4 in, 33 lbs) are designed as premium sauna heater stones that combine smooth steam performance with a natural, river-rock appearance. Formed from durable olivine diabase, each 2–4 inch stone withstands repeated heating cycles while holding and releasing warmth steadily for a more relaxing löyly. Their rounded contours promote excellent air circulation within the heater basket, allowing electric and wood-burning units to heat efficiently and respond evenly when water is poured over the stones. The 33-pound box provides a convenient quantity for topping off existing rock beds or creating an attractive surface layer that softens the look of angular base stones. Ideal for owners who want both dependable heat distribution and a more organic, spa-like aesthetic, these Harvia rounded stones elevate everyday sauna sessions.