Sauna stone types compared: olivine diabase, vulcanite and granite

Sauna stones come under a handful of rock names. Olivine diabase is the one Harvia calls the most common and used. The rest are variations on it or alternatives to it. Here's what each name means, according to the makers and reference pages.¹

What to have in hand

• Your heater's manual, open at the page about stones.
• The stone type and size range the maker names for your model.
• The product page of any stone you're thinking about, so you can compare names.

The rocks you'll see named

Olivine diabase

Harvia says this is the most traditional type of sauna stone. It says the structure withstands strong temperature changes.²

HUUM also sells olivine diabase stones. It says they're enduring and their thermal capacity is high.³

The names are a little tangled. Wikipedia says diabase is the preferred name in North America, while dolerite is the name in the rest of the English-speaking world. So a UK or Australian page may say dolerite.⁴

As for the "olivine" part, Wikipedia lists minor olivine in diabase, from 3% up to 12% in olivine diabase.⁴

Heat-treated stones

Some stones get extra processing. Harvia's Elite Pro Heavy Duty stones are olivine diabase exposed to temperatures of approximately 1000 degrees Celsius.¹

Longer life is the point. Harvia calls this type optimal for public saunas with intensive use. That's a different job from a family heater. Check what your own manual allows.¹

Peridotite

Wikipedia defines peridotite as a dense, coarse-grained igneous rock made mostly of the minerals olivine and pyroxene.⁵

Neither Harvia's nor HUUM's pages cited here list peridotite as a heater stone. Olivine diabase is a different rock: a diabase with some olivine, 3% up to 12% according to Wikipedia.⁴ If a label says only "peridotite", your manual is what says whether the maker accepts it. Ask the maker if it's silent.

Vulcanite

Harvia says vulcanite is hard and durable and doesn't differ much from the traditional stone. Its special feature is color, very dark, and almost black when wet.²

Round or angular

Round is a shape, not a rock. Fair enough, but it still shows up on labels as if it were a type. HUUM recommends round stones because they provide milder steam.³

Harvia's rounded stones are olivine diabase too. Its pages recommend larger standard olivine diabase stones in the bottom layers and rounded ones on top.¹

Decorative stones

Harvia's white and red granite stones are made as decoration for the top of the heater. Its pages say white stones are for the top layer only.¹

What to do with this

Write down the rock name and the size range from your manual. Then look at size and stacking. Garden rocks are a different case, covered in why garden and river rocks are a bad idea.