Sauna stone types compared

Up to date as of October 24, 2026

Most sauna stones sold today are olivine diabase. Harvia calls it "the most common and used sauna stone for all heater types"¹. Besides olivine diabase, Harvia also sells heat-treated olivine diabase, rounded olivine diabase, black vulcanite, and decorative white stones and decorative red granite stones.

The main kinds

Stone	What the maker says
Olivine diabase	Harvia describes it as a subvolcanic rock mined in Western Finland¹. HUUM says it's enduring and has a high thermal capacity².
Heat-treated olivine diabase	Harvia says the heat treatment gives the stones a longer service life, and calls them optimal for public saunas with intensive use¹.
Black vulcanite	Harvia describes a small granular, dark grey stone¹.
Rounded olivine diabase	HUUM says round stones provide milder steam².
Decorative white stones and red granite stones	Harvia sells each for the top layer only, at a maximum of one box per heater¹.

Not sure what the rock names mean? The rock names page sorts them out.

Shape matters too

Stones come angular or rounded, and some heaters call for one shape. HUUM recommends round stones for its heaters². Harvia says some of its heaters require round stones as well³.

Your manual decides. Not the shop, and not what your neighbour used.

Rounded on top, rough below

Harvia says rounded olivine diabase on the top layer lets poured water run easily down to the lower stone layers¹. For the bottom layers it recommends larger standard olivine diabase stones, because they give more heating surface area for the water¹.

HUUM makes a similar point from the other side. It says the round shape ensures water reaches the inner stones and evaporates gradually, instead of vaporizing in one go from the top layer².

So a mix can make sense. But only if your heater's manual allows it.

Hard, dark and durable

Harvia says black vulcanite is a good choice for a sauna stone because it's hard and durable¹. It also says that when wet, the stone shines black¹.

Heat-treated stones are a different idea. Harvia says its Elite Pro stones are olivine diabase exposed to approximately 1000 Celsius, and that this treatment gives longer service life¹. It calls them optimal for public saunas with intensive use¹.

Decorative stones

Decorative white stones and decorative red granite stones are sold for looks. Harvia says each is for the top layer only, at a maximum of one box per heater¹. Think of them as trim. They aren't the main fill.

Why you shouldn't pick your own

It's tempting to fill a bucket at the river. Don't. Harvia says many stone types are unsuitable for a sauna because they contain dangerous toxins or can't take big temperature swings³. It also says finding safe stones in nature isn't simple if you can't recognise stone type and quality³.

Harvia says its own stones are tested by the Geological Survey of Finland³. That's one maker's claim about its own product.

Buy stones sold for sauna heaters. Then check the size against your manual, which the size page walks through.

Start with the heater maker, not the rock.

Cited material

Harvia sauna heater stones, Harvia
Sauna stones, HUUM
The easy guide to looking after your sauna stones, Harvia