Peridotite, olivine and diabase stones

The labels are confusing because the same rock goes by several names. Here's what each word means, and what the heater makers actually sell.

Olivine

Olivine is a mineral, not a rock. Wikipedia says it's the essential mineral found in all peridotites¹. The magnesium-rich kind is typically olive-green in colour¹.

So when a bag says "olivine", it's naming an ingredient. You still need to know what rock it's in.

Peridotite

Wikipedia describes peridotite as a rock containing olivine¹. The maker pages cited on this site sell olivine diabase and don't list peridotite. If a bag says peridotite, check your heater's manual for the stone types it accepts before you buy. Don't guess.

Diabase

Diabase is a subvolcanic rock, and it's also called dolerite². Wikipedia notes that diabase is the preferred name in North America, while dolerite is the preferred name in the rest of the English-speaking world².

That matters if you shop across borders. A UK or Australian listing may say dolerite where a US one says diabase.

Olivine diabase, the common one

Put the two words together and you get the stone most makers sell.

• Harvia names olivine diabase as its traditional stone type, the one it says is used across all heater types³.
• Harvia says it's durable in structure and, thanks to high density, stores and releases heat well³.
• HUUM describes its olivine diabase stones as enduring, with a high thermal capacity⁴.
• Sauna from Finland, an industry network, names olive diabase from the Satakunta region of Finland and says the Geological Survey of Finland controls the quality of the stones it describes⁵.

Thermal capacity just means how much heat a stone can hold.

Other names you'll meet

Olivine diabase isn't the only line on a maker's page.

• Heat-treated diabase. Harvia sells olivine diabase that has been exposed to approximately 1000 Celsius, and says the heat treatment gives the stones longer service life³.
• Vulcanite. Harvia describes black vulcanite as a small granular, dark grey stone³.
• Rounded olivine diabase. Same rock, shaped round. HUUM sells round olivine diabase stones in 3 to 5 cm and 5 to 10 cm sizes⁴.

So the rock name tells you what it's made of. Words like "heat-treated" or "rounded" tell you how it's been prepared or shaped.

What to do with all this

Don't shop by rock name alone. Harvia says to always check the right stone size and amount from the manual that came with the heater³.

If the manual lists a stone type, buy that. If it names a size, buy that too. The size page and the stone types page cover the next steps.