Rock Dust

SOME rock dust is absolutely the cheapest way to buy in critical nutrients NECESSARY for agriculture, while SOME rock dust might be bogus, in SOME soils.

exactly, imo this how everything is in permaculture/natural farming. It might work good or great somewhere, but somewhere else it sucks or is plain bad.

In my personal experience rock dust is a must. I had a bed that was 2' x 3' and all I filled it with was peat, compost, rice hulls, and rock dust... nothing else not even a nitrogen source. The plants were huge lush green and without pests or deficiencies. The yield was great and flavor converted some tomato haters.

That's almost exactly the mineral route I'm taking. I don't have the bedrock issue but there are pits on my road which process glacial till into crushed rock.

The glacial rock is a mixed bag of mostly igneous rock. Stone dust is cheap and it makes for quick path building.

When dust paths are built , they will get mixed with the soil over time. Normally efforts are made to prevent loss of pathway gravel to the surrounding soil. With stone dust, It's not a problem.

Oops, the thing like my plan is at the end of page 1 which I thought was the end of the thread. Anyway, some would be mixed with manures and compost and in the bedding for animals. The ideas is to allow chemical and microbial action free up nutrients. The animals will stomp their manure into the stone dust.

Poultry will be offered granite grit. Their gizzards are nature's grist mills.

The stuff is cheap so I'll order the biggest dumper for the bulk savings. Whatever isn't used immediately will keep until forever.

I don't much like digging up old threads, but I don't see much discussion on rock dust, and there's some important points that need to be laid out.

First, for the doubters, some interesting facts. As glaciers slide across the earth, they naturally leave a trail of boulders, gravel, and powdered rock called "rock flour", which quickly washes and blows away. This rock flour eventually settles in various places, collecting in dunes and sometimes covering large areas. After being rained on a bit, it partially calcifies and becomes a soft sandstone-like sediment called loess.

Structurally, loess is a farmer's nightmare. It is stiff and crumbles into dust, erodes extremely easily, and is porous to the point where water practically falls straight through it.

In spite of this, in coincidence with favorable climates, loess is the most agriculturally productive soil in the world. Loess defies everything you think you know about soil. Loess with zero topsoil and zero OC is equally productive as loess with 10ft of topsoil. Plants can extract literally 100% of the non-N nutrients they need directly from the rock particles, and easily enough so to attract farmers from every civilization that has encountered it. Even more extraordinary, loess retains its fertility over geological timescales; the loess plains in China have been under continuous cultivation for over 1500 years with zero inputs. All of the deep rich soils in the central US and middle and eastern Europe formed on top of loess. In places where it isn't overlain by topsoil, it's a mind trip to see plants sprawling happily out of what looks superficially to be dead sandstone or clay.

People here and in general seem to have the idea that rock dust is something that requires some kind of extra processing in order to be available to plants, either having birds eat it, running it through composting, or by whatever other means, and then after a few years they figure you'll have to add more. This is pretty close to the opposite of the truth. In reality, the nutrients in rock dust are very immediately available to plants (given a good colony of root symbionts) and very insoluble in water and resistant to leaching. You can grow plants in pure rock dust, and they will flourish (although the texture is bad for water retention) and can acquire all the nutrients they could possibly need to grow at any rate purely from the rock dust - no organic material required. Moreover, the fertility of rock dust will outlast you, your children, grandchildren, and probably any biochar you might make. Rock dust can literally convert ancient soils into brand new soil; proponents often refer to it like it's magic, and they're really not so far off. Ten or twenty years of applying a bit of rock dust to your land and you can farm it more or less forever. You might call it permanent fertilizer (permalizer?).

Some words of caution: DO NOT USE GRANITE. Granite contains on average twice as much uranium as other rocks, sometimes more, as well as high levels of thorium. It's also less than spectacular in terms of nutrient value.

Some good rock dusts: Azomite, although expensive, has a very high and well balanced nutrient value. It seems like perhaps they have geologists picking out rocks of agricultural interest specifically or else they are just very lucky. Glacial rock dust or ground river rocks are also very good. If your property is all rocks you might also consider grinding them to have something to plant in.

Another thing that's been mentioned here, although incorrectly, is greensand. Greensand is a sedimentary rock that forms in shallow ocean waters, by the accumulation over geological time of kelp and other marine organisms. Greensand is high in K and sometimes has significant amounts of P. It also has substantial Ca and Mg, and micronutrients similar to kelp meal, but more concentrated and extremely slow release.

I think, in recovering chemically leached soils, in rejuvenating old weathered soils, or just because you want some vegetables that have nutrients in them, rock dust and greensand are like bread and butter. Some people seem to see it as cheating, but I would consider them fundamental to permaculture. After all, it's not like we're going to run out of rocks any time soon.

EDIT: I retract what I said about Azomite, I was reading the numbers wrong. There is no significant difference between Azomite and glacial rock dust or any other (non-granite) rock dust. Since rock dust has a very balanced nutrient profile, the advantages of greensand are less for nutrient value (although it can be quite respectable) and more in cost and water holding capacity. In acidic alfisols, ultisols, and oxisols, adding biochar with rock dust will help raise the pH. Rock dust has a pH of ~7.6, and it can take quite a lot to neutralize acidic weathered soils, which have pH values as low as 4.0.

M Troyka wrote:...Loess with zero topsoil and zero OC is equally productive as loess with 10ft of topsoil.

We don't observe that. There are 45 feet of loess beneath us, according to the well driller's log. It's great stuff, but there is no comparison between what grows on bare loess and what grows on biologically active soil here.

M Troyka wrote:Another thing that's been mentioned here, although incorrectly, is greensand.

It wasn't greensand being mentioned; it was greenstone, which is a type of basalt.

I would imagine conditions in alaska would be very different than for loess in other climates, although maybe not? I would assume at least that black dirt would give you a longer growing season than pale loess would. OC might also hold more water, but I don't know about that, either.

I'm not sure about greenstone either. There's only a few things called "greenstone", most of which are serpentinite based, and serpentinite is poisonous to plants. Chlorastrolite is a possibility, but is almost always used as a decorative stone, and greensand is also called greenstone. I would assume highest likelihood is that they're talking about greensand.

M Troyka wrote:I would imagine conditions in alaska would be very different than for loess in other climates, although maybe not? I would assume at least that black dirt would give you a longer growing season than pale loess would. OC might also hold more water, but I don't know about that, either.

It's not a matter of season length or moisture availability; plants growing on living soil here are far more vigorous and healthy than those grown on bare loess, which is our subsoil. Loess here is generally regarded as originating from glacial silt, which has been wind-deposited in its present location.

M Troyka wrote:I'm not sure about greenstone either. There's only a few things called "greenstone", most of which are serpentinite based, and serpentinite is poisonous to plants. Chlorastrolite is a possibility, but is almost always used as a decorative stone, and greensand is also called greenstone. I would assume highest likelihood is that they're talking about greensand.

I assume the highest likelihood that he at least thought he was talking about basalt, since he said so:

"...I will try the Basalt dust - it is also called Greenstone as I can deduct."
"Thats why they use Greenstone (Basalt)"

Greenstone is altered basalt. From About.com:'

"Greenstone is a tough, dark altered basaltic rock that once was solid deep-sea lava. It belongs to the greenschist regional metamorphic facies.
In greenstone, the olivine and peridotite that made up the fresh basalt have been metamorphosed by high pressure and warm fluids into green minerals—epidote, actinolite or chlorite, depending on the exact conditions. The white mineral is aragonite, an alternative crystal form of calcium carbonate (its other form is calcite)."

Greenstone dust is currently being sold as an agricultural amendment. From http://bogi.org.au/local-rock-dust:

"Igneous Metamorphic Rock

Basalt, Greenstone, or Hornfels rock dusts provide calcium, magnesium, and phosphorous. They also provide many other valuable trace elements such as iron and silicon.

The following Brisbane area quarries mine igneous metamorphic rock:

Boral Petrie quarry (Greenstone)
Boral Narangba quarry (Greenstone)
Boral Purga quarry (Basalt)
Boral Narangba quarry (Hornfels)"

The link you listed seems to suggest a distinction between greenstone, basalt and hornfels. I think "greenstone" may refer to "greenschist", which apparently contains significant Mg and Ca. (also chloride and sometimes sodium)

Also, it may be possible that the "bare loess" in your area is depleted of minerals. I've heard of that occurring in some places, often by human meddling, but I think it generally occurs when mineral rich organic matter erodes off of its spent subsoil.

M Troyka wrote:The link you listed seems to suggest a distinction between greenstone, basalt and hornfels. I think "greenstone" may refer to "greenschist", which apparently contains significant Mg and Ca. (also chloride and sometimes sodium)

Also, it may be possible that the "bare loess" in your area is depleted of minerals. I've heard of that occurring in some places, often by human meddling, but I think it generally occurs when mineral rich organic matter erodes off of its spent subsoil.

Yes, there is a distinction; I was merely pointing out that the original poster believed he was talking about basalt. Greenstone is an altered basalt, and although sometimes used as a synonym for greenschist, is distinct:

"GREENSTONE and GREENSCHIST

Greenstone:
Greenstone is a non-foliated metamorphic rock derived from basalt or chemically equivalent rock such as gabbro. Greenstones contain sodium-rich plagioclase feldspar, chlorite, and epidote, as well as quartz. The chlorite and epidote make greenstones green.

Greenschist:
A grade of metamorphism characterized by abundant chlorite and schistosity. Greenschist "facies" metamorphic rocks are produced under relatively low temperature-pressure conditions.

-- Excerpts from: USGS/NPS Geology in the Parks Website, 2001, and Geology in Michigan Glossary, State of Michigan website, 2003"

Loess varies in composition. The loess up here is regarded as fertile, but I don't see how it could possibly expected to perform well without nitrogen supplementation, and there are likely other minerals that are unavailabe sans biological mediation.

We've used rock dust for new plantings on our plot here in Devon, England these last three years, though without any kind of control to determine how much of a difference it alone makes. Over the same period we've been using locally produced mycorrhizal innoculant too, which could also affect what we've seen; our plants are generally growing well, even where they have had to be planted on a fairly steep, scrubby slope (which we can't modify as it's a guerrilla planting).

One thing is certain, postage for such heavy material is expensive. A £20 bag of rock dust from the Seer Centre in Scotland cost another £20 to deliver, certainly not a low-EMERGY material - at least not where it isn't locally available. That said, we know that a good diversity of minerals are important for life, ourselves included and most shop-bought industrially produced food lacks many of these. Having such efficient fertility-removal systems (er, toilets) ensure that what comes out rarely goes back in. So until we fix that issue, investing some energy in improving our zone 1 soils to enable us to meet more of our nutritional needs locally and reduce what we need to import from further afield is a worthwhile expense we feel.

Of course, adding organic matter to feed the soil life usually gives the greatest improvement for the least effort, but minerals are important too. Dynamic accumulators have already been mentioned and in my experience, those plants often considered rampant weeds are actually there to repair the damage done by us. These plants, which I see to be nature's paramedics, are often those best adapted to seek out and accumulate the very mineral elements that have been depleted, often only leached down to lower levels. Because these plants are so good at finding these elements, they have an advantage over the others and are well placed to exploit this niche. Over time they pump the missing minerals back to the surface through their process of annual leaf drop and surface root shedding. As the topsoil becomes better balanced again, succession will overtake these specialists and biodiversity increases. Alas, most folks dig out the very plants that are there to repair the damage to try and grow others less well adapted to these challenging conditions. I figure that a good compromise is making a liquid feed from a patch of accumulators to feed any areas of soil that have been cleared of these pioneers to grow other plants.

It's worth remembering too that pH affects how accessible different elements are to plants and so those that appear to be missing may simply be 'locked up' in the soil. Here's an important chart that shows the effect of pH on availability:
http://www.pda.org.uk/image/leaflets/24/truog_pH_chart.jpg

Adding rock dust to quickly improve soils may still be a good investment of what fossil fuels we have left though. Especially given that it is a waste product of the quarrying industry.

As to how effective it is, I'm still unable to say. One interesting book on the subject though is 'Paramagnetism' by Philip S. Callaghan (Acres USA). His experiments showed that materials with a high paramagnetic value appeared to be of significant benefit to plants and animals. Some rock dusts, basalts in particular, do have high paramagnetic values and this may be one of the reasons why it has been shown to be a beneficial soil additive, though not all rock dust is the same in this respect, different quarries produce dust of different values. Which is where it gets complicated again as there are many potential sources of rock dust and a special meter is required to take these readings.

So forums like this become an important hub for us to all share what's working for us (such as sources of rock dust that seem to really help) and to increase the value of our own experiences. As such it's great to see so many folks on here getting on with making the world a better place.

Aranya wrote:One interesting book on the subject though is 'Paramagnetism' by Philip S. Callaghan (Acres USA). His experiments showed that materials with a high paramagnetic value appeared to be of significant benefit to plants and animals. Some rock dusts, basalts in particular, do have high paramagnetic values and this may be one of the reasons why it has been shown to be a beneficial soil additive, though not all rock dust is the same in this respect, different quarries produce dust of different values. Which is where it gets complicated again as there are many potential sources of rock dust and a special meter is required to take these readings.

You got me googling when you mentioned paramagnetism and from what I'm understanding of this, the paramagnetic material doesn't even need to be in contact with the plant roots to be effective (tests using film canisters filled with paramagnetic dust, etc). I'm wondering if it might be worth testing larger stones, rocks and boulders for paramagnetic properties and placing them strategically to enhance the effect rather than purchasing rock dust that has these properties. Heck, maybe that's part of Sepp's secret!

Very interesting discussion on the rock dust though. I've read about it a bit in the past but never took much time to dive in and do the research until reading this thread here. This forum definitely aids in adding wrinkles to the brain

Eliot Coleman has great rock dust recommendations in his book The New Organic Grower. I'd recommend it for a well researched opin on the issue

I'm in Florida and grow in sand. Now, I've been adding tons of organic material to my sand and have a nice black layer going but someone mentioned that rock dust is useless with sand. If I have some organic material is it worth me getting some rock dust? Or will it leach through the sand with little uptake?

Thank you!

Both Azomite and Gaia's Green sell their products in two forms: pulverized, and granulated.

For a sandy soil, I would choose the granulated size, as it won't 'wash' through with the first few rains.
With plenty of organic matter in the soil, the rock dust should stick around for a while.
The soil critters will also be munching on the rock dust, thus helping to keep it in the active zones.

Rock dust adds minerals to your soil, it is really great stuff. But my problem, and this is not the right place for this is that I have trouble getting on your site and leaving my comments, although they may be inane, the world has to get off of where it is at or change will come. So what does a person against violence try to get their message across.

Aranya wrote:

Of course, adding organic matter to feed the soil life usually gives the greatest improvement for the least effort, but minerals are important too. Dynamic accumulators have already been mentioned and in my experience, those plants often considered rampant weeds are actually there to repair the damage done by us. These plants, which I see to be nature's paramedics, are often those best adapted to seek out and accumulate the very mineral elements that have been depleted, often only leached down to lower levels. Because these plants are so good at finding these elements, they have an advantage over the others and are well placed to exploit this niche. Over time they pump the missing minerals back to the surface through their process of annual leaf drop and surface root shedding. As the topsoil becomes better balanced again, succession will overtake these specialists and biodiversity increases. Alas, most folks dig out the very plants that are there to repair the damage to try and grow others less well adapted to these challenging conditions. I figure that a good compromise is making a liquid feed from a patch of accumulators to feed any areas of soil that have been cleared of these pioneers to grow other plants.

Thank you very much! I have been trying to make this exact point without much luck getting it across.

Rick Larson wrote:

Aranya wrote:

Of course, adding organic matter to feed the soil life usually gives the greatest improvement for the least effort, but minerals are important too. Dynamic accumulators have already been mentioned and in my experience, those plants often considered rampant weeds are actually there to repair the damage done by us. These plants, which I see to be nature's paramedics, are often those best adapted to seek out and accumulate the very mineral elements that have been depleted, often only leached down to lower levels. Because these plants are so good at finding these elements, they have an advantage over the others and are well placed to exploit this niche. Over time they pump the missing minerals back to the surface through their process of annual leaf drop and surface root shedding. As the topsoil becomes better balanced again, succession will overtake these specialists and biodiversity increases. Alas, most folks dig out the very plants that are there to repair the damage to try and grow others less well adapted to these challenging conditions. I figure that a good compromise is making a liquid feed from a patch of accumulators to feed any areas of soil that have been cleared of these pioneers to grow other plants.

Thank you very much! I have been trying to make this exact point without much luck getting it across.

I think there are valid points to that, and dynamic accumulators definitely play an important role in mineral management of soils, but I also think that's largely missing the big picture message. Organic material like compost is not only inefficient for supplying minerals to soil, it's downright impractical. In order to provide sufficient calcium, for example, would require that you import 4,500 tons of compost per acre. Not only is that unaffordable to basically everyone who matters, but it would produce a rather sizable mountain of compost on the land out of which most plants will be unable to obtain sufficient calcium due to the sheer depth. Additionally, levels of other minerals besides calcium would be significantly out of balance with shortages of magnesium and other elements, and the results of that input would be temporary at best. (you can do the same with around 1/1000th that amount of coarse ag lime)

Over 50 years ago, from about 1930-1950, the government was having a fit because of the loss of topsoil in the dust bowl, and so began encouraging the beginnings of what is now known as soil science. At that time, William A. Albrecht and a few other big names (who have since been buried by the government and chemical companies, who didn't hear what they wanted to hear) were already complaining that 60 years of exploitative farming had cut the mineral content of the mineral-rich glacially fertilized midwest down by half. In the 50+ years since then those values have fallen in half yet again. Albrecht noted that rates of diseases like heart attacks, dental caries and cancer varied inversely with the mineral content of the soil, and had been increasing linearly during the time when those soils were being depleted. Places where the soil hasn't had mineral content in millions of years, ie the east coast where I live, have always had chronically higher rates of these diseases and others.

Plants are only capable of extracting the mineral content that is there. Plants can fix all the carbon and nitrogen they need from the air (although the nitrogen in organic matter is higher quality), no amount or type of organic methods have the capability of creating even one ounce of calcium, magnesium, copper, zinc etc. We have been removing these things from our soil for the last hundred years, sending it down to someone else's "sewage treatment plant", and then from there dumping it into the ocean. Even with 20 years of dynamic accumulators you might be able to wring half of the mineral content needed for human health from the soil, but even then every pound of food you sell is an ounce of minerals that are as good as gone forever. They need to be replaced only once every decade or two, but they do need to be replaced by some means. "Zero input" is not sustainable, at least not if growing food as medicine is important to you.

That aside, another important fact I've come across is that rock dust alone is a poorly balanced mineral supplement. It generally doesn't have enough calcium for the magnesium it contains, it's utterly deficient in phosphorous, and may need a small amount of greensand or similar for potassium. Fish/seaweed meal is still needed as well, for the iodine and selenium, which are only present in relatively small quantities in rock dust. If you could afford to replace all your soil with rock dust, that might be less of a problem, but in practical terms it will need balancing and supplementation, and if you don't know how to interpret a soil test you will not know what needs to be done or why.

I have heard/read (can't remember which) that most places on the planet have a complete complement of minerals in the subsoil. I am not sure as to the truth of this statement but considering that soil analysis only takes into account the soil and not the subsoil it may make sense that we can supply our mineral needs without outside inputs. I am not sure either way but what I do know is that rock dust applied to my soil has given me some pretty amazing gardens. Gardens which produced and were lush when others struggle with odd weather and poor yield. For example two years ago we had a very odd season. At the time I worked at a large local nursery so I got to hear a lot about how people's gardens were doing. Time after time people would come in complaining about their garden not doing well. I could only think/respond that my garden is doing great. Plants grew rapidly, the yield was high, and the flavor was great. Perhaps a complete fertilizer can be had with rock dust, soft rock phosphate, and green sand. Either way I would like to setup a system where the application of the aforementioned would only take place during the establishment of a garden or paddock (3-5 year). I was thinking of starting to add granulated rock dust to my seed mix so that when I sow my seeds the area also gets a dose of minerals. I sometime use sand or small rock for this anyway.

A soil test takes into account whatever you put in the bag and send in to get tested. If you want to know what's in your subsoil, dig down to it and send that in. Once you've balanced the mineral content in the soil you've got already, you only need to add a maintenance dose of minerals maybe every 20 years if you don't want to do anything more often than that. As long as you've got a good ground cover you don't need to till it in or anything, either.

Also, it's interesting you should mention plant health, as Dr. Albrecht also noted that plant diseases most often stem from nutrient deficiency, otherwise a healthy plant will protect itself adequately. I suspect this is the mechanism of action for biodynamic sprays, since they use dynamic accumulators like horsetail and stinging nettles to make their teas, they probably provide minerals to the plants that would otherwise be deficient. If that is the case, then mineralizing properly should prevent things like fusarium from eating up your squashes and things only without any spraying or fussing. I'll be testing that next year, and I've got the perfect hot+humid mold climate for it, too. We have yet to have a single year here where the cucumber plants didn't die off or at least lose every leaf from some form of mildew or other.

Not all rock dust is the same. The stuff you might get for free from quarry operations is usually quite limited in its contents.

Dedicated agricultural amendments such as Azomite or Gaia's Green typically have more minerals and trace elements than generic rock dusts do. I would suggest getting a thorough soil sample first, to see what minerals are lacking before spending a lot of money on a product that may not solve your problem - or worse yet, applying a mineral that already exists in excess.

Here are sample breakdowns on the contents of both Azomite and Gaia's Green. As you can clearly see, they differ widely as to contents and quantities. Your needs should be the deciding factor, rather than price. You may need to buy individual elements to fulfill deficiencies.

Azomite

Gaia Green

EDITED to update Azomite link. Gaia's Green no longer is sold (at least under that name). JP

Bumping this ahead. It's the best thread I've seen on rock dust. I have no shortage of rock dust since I'm on glacial till over 100 ft deep in nearby gravel pits, with everything from rock flour to 100lb+ nuggets. I'm adding some clay, since it helps with soil structure and water retention when rock flour makes up a large proportion of the base soil. I used to assume that rocky ground equaled deficiency. My dad's place has very little rock, being in a sandy zone of an old lake bed. His ground is easy to work but must have mineral supplements for good production. Everything seems to grow in gravely rock flour that has compost on top.

i like diatomaceous earth.
its VERY fine. a powder really.
thats means its more available to micro-organsims. and its mostly silica
but also has lots of micro-nutes.
worms seem to love the stuff
add it to compost and the organisms break it down first and release the nutes and silica.
my papaya and other herbaceous plants and seedlings have shown huge growth spurts with it.

ive used glacial rock dust, and 2 or 3 others
but they didnt have the same effect
the glacial was fairly fine, but not as fine as the DE.

ive never tried Azomite.
is it as fine as DE ? or as Glacial RD ?

Diatomaceous earth is mostly silica, which is, for the most part, chemically inert. That means there is little, if anything, available for biologic processes. I don't agree that adding DE will improve a soil's mineral content in any meaningful way.

Rock dust, in general, can be extremely helpful, extremely harmful, or anywhere in between. It all depends on the existing soil conditions and the composition of the rock dust. Adding limestone rock dust to an alkaline soil isn't going to help you. Soil pH is extremely important to nutrient uptake.
There is much bad information here. There is also some very good information.

Rock dust can only assist if the existing soil is deficient in minerals, pH imbalanced, etc, which can be improved by the rock dust.
However, rock dust can drastically (which can be beneficial or harmful) alter the pH, structure, and nutrient availability (both positively and negatively) of the soil. If you randomly add rock dust (or any other soil amendment) without knowing the existing soil's chemical balance, pH, and structure, you stand as much chance of causing a serious problem as you do of making an improvement.

Hi- continuing an old thread - but I wanted to pick up on the comment about using river sand as a rock dust.  The closest source of rock dust is three hours away, but 1-2 times a week I go to a monastery church in the valley of the Tararua Ranges (New Zealand), and there is a river beside it with rocks and sand of various size for the taking.I don't know what type of rock it is (though I do know it is dredged into huge piles and collected nearby by the truckload - I think by a road-building company), but I am wondering if I can only do good by collecting a few buckets of sand each trip and spreading it round our 8 acres.  We are near the ocean on very flat land.  We have sandy soil, but no mountain run-off.

It depends on the local geology. You are looking to replace trace minerals that are missing in your top soil. In most cases they are missing through a combination of water/chemical leaching due to weathering, and due to their absence the in the underlying rock. If the river sand is derived from the same rock as your garden it is unlikely to add much. If, on the other hand, it is from a volcanic rock it will likely have lots of good stuff in it.

Google should help you find geologic maps of your area.

On the other hand, it can't hurt beyond wasting some of your time and effort.

Annie Hope wrote:Hi- continuing an old thread - but I wanted to pick up on the comment about using river sand as a rock dust.  The closest source of rock dust is three hours away, but 1-2 times a week I go to a monastery church in the valley of the Tararua Ranges (New Zealand), and there is a river beside it with rocks and sand of various size for the taking.I don't know what type of rock it is (though I do know it is dredged into huge piles and collected nearby by the truckload - I think by a road-building company), but I am wondering if I can only do good by collecting a few buckets of sand each trip and spreading it round our 8 acres.  We are near the ocean on very flat land.  We have sandy soil, but no mountain run-off.

Carrying 1-2 Kg would be okay but any other amount larger than that may disturb the eco system. Please be careful when removing material from other eco systems.

Also if it is not in powder form (like flour) it may not work straight away.

Why not look into liquid fish fertilizer? Some wild caught fish carcasses fermented with kefir or any other yeast would give you a lot of minerals as well as nitrogen. I prepare in 20L buckets and even the large thick heads dissolve into the water in 5 months.

The deal is that the different types of rock can have contradictory properties and thus different positive effects in the soil. Not necessarily complimenting one another but inhibiting.
So it is more effective to add one just one type of paramagnetic rock powder per year.

-Organic Horticulture Specialist