I've heard many people talk about using rock dust when talking about organic gardening.

From what I understand rock dust is made from crushed rocks. If they are to be used in an organic garden I assume they are made from real rocks; rocks that took many years to form.

It would seem to me that using rock dust is less sustainable than using something like sustainable timber. I would appreciate if someone could explain whether using rock dust is a sustainable practice or are we using up a irreplaceable resource?


On the off-chance that you're serious...

No, we are not in danger of running out of rocks. Erosion eventually deposits the sand and mud in the bottom of the ocean, and when it gets deep enough it makes rock again. That gets uplifted, either through tectonic uplift or volcanically, at which point erosion goes after it again. Almost any rock you see has been through this cycle a few times. Fossils of ancient sea creatures are found in the Himalayas.

Much more significant is the energy used (and carbon emitted) to remove, transport and crush the rock.

I don't know how you would use sustainable timber in lieu of rock dust. You might explain that.

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  • As well, rock dust is reusable in cement and other building supplies so it is not quite the same as wood that decays. – kevinsky Jun 5 '12 at 14:29
  • It does seem like a silly question at first, but the more I thought about it, the more it became an interesting what-if thing to ponder. I agree, we live on a big rock, so we'll always have rock, but one could argue (completely in hypotheticals) that we might crush rock faster than nature can replenish it. – DA. Jun 5 '12 at 16:53
  • @DA They're trying to do that in parts of West Virginia and Kentucky.;-( But it can't be done without a much larger source of energy. Just the tectonic uplift in the Himalayas lifts over 10 trillion kilograms of rock above sea level per year, by my reckoning. If you want to worry about losing rocks, I'd worry about them drowning (global warming) first! – Ed Staub Jun 5 '12 at 17:56

I think there are specific types or sources of rock dust that you are referencing here, such as glacial rock. This is often collected in either dust form or in rock form that is then ground to dust. The reason this source is used is the nature of glacial activity - it collects rock from many sources along its path and consequently it has a wide but perhaps inconsistent mineral content.

So while a particular source location might not be considered non-renewable, I would say that the material in a more general sense is very, very renewable.

I've also heard of people putting rock dust in their worm farms as worms require substances like this in their gizzards to help grind down plant matter. Apparently they don't have teeth. Who knew?

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Living, growing trees also sequester carbon dioxide and give off oxygen - removing them from the biome as living organisms increases the carbon dioxide load on the atmosphere, as the microbes that cause wood to decay expell carbon dioxide or methane as part of their respiration process (yes, even single cell organisms need to "breathe"). Also, "sustainable" timber usually requires pesticides and fertilizers, which are generally petroleum products with net negative effects on the environment.

Rocks are heavy and hard and need to be quarried, moved around and ground into dust. This requires energy - but it's hiiiighly unlikely it requires more energy than cultivating, harvesting and processing trees for the same purpose. Definitely not more ecological in the aggregate - so grinding up rock is more sustainable.

Plus, the entire planet outside of its small iron core is made out of rock.

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