Starduster Society

Here is an excerpt from Dr. Supkow's eye-opening book, Rock Dust and the Environment. You may publish, on your web site or elsewhere, this excerpt in its entirety, with no omissions or editing, if you include the following statement, "You may obtain the eye-opening book, Rock Dust and the Environment, for $10.00 postpaid from Starduster Society,, 28 Sefton Circle, Piscataway, NJ 08854, USA. (Foreign addresses require additional postage.) Signed, Donald J. Supkow, President Starduster Society, a non-profit 501(C)(3) organization for which donations are tax deductable." Back to Starduster Society Main Page,

Index: What is Rock Dust? What is Rock Dust Used For? What are Rock Dust's Other Benefits?
What is Rock Dust's Effect on Pollution and Ozone? Where can Rock Dust be Obtained?
How does Rock Dust Bug Bugs? What are the Additional Chapter Titles?


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What is rock dust?

Rock dust is a common name for finely pulverized rock.

How fine is fine?

The finer, the better, practically, 90% finer than 200 mesh.

What does 200 mesh mean?

That is a standard designation for a sieve having 200 openings per linear inch. Particles which pass through a 200 mesh screen have a maximum diameter of about 74 microns (0.0029 inch).

What kind of rock is rock dust made of?

Commonly, most types of igneous or volcanic rock such as granite, basalt, diabase, granite gneiss and volcanic ash, OR gravel containing particles composed of any combination of the above rock types.

What is rock dust used for?

Rock dust is used for agricultural and horticultural purposes to improve the quality of all soils. Some rock dust is also used as an animal feed additive.

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Why do I want to improve the soil quality?

To help plants to grow better. The better the soil quality, the better plants grow.

Why is rock dust added to animal feed?

The rock dust helps the animals digest their food better, makes them more productive, improves their health, and improves the quality of the manure they produce.

How do they pulverize the rocks to make rock dust?

Most rock dust is not a result of deliberately crushing rocks to produce rock dust. The rock dust is a by-product from rock quarries that crush large rocks to make little rocks to be used for making concrete, black top for roads, and for other purposes requiring crushed stone. Some crushed stone, such as railroad ballast, is washed to remove residual traces of rock dust. Dust in the air resulting from the crushing operations is often caught in a large filter which operates like a very large vacuum cleaner, called a bag house.

Does rock dust contain all the trace elements needed by plants?

No. Most rock dust contains only negligible quantities of nitrogen and carbon.

Where do plants get the nitrogen and carbon that they need?

Even though the air contains about 80% nitrogen, the atmospheric nitrogen is not directly available to plants. The nitrogen must first be fixed into a form that is useable by plants. The process of fixing nitrogen is carried out by bacteria which exist naturally in many soils. Soil bacteria are composed of protoplasm, which contains protein, of which nitrogen is an essential component. If the bacteria content of the soil is increased, the nitrogen content is automatically increased. Some plants, primarily legumes such as beans, alfalfa and clover, have nodules on their roots which harbor colonies of nitrogen fixing bacteria. Some atmospheric nitrogen is fixed by lightening during electrical storms. Some nitrogen is fixed by high temperatures and pressures within internal combustion engines. The fixed nitrogen which enters the atmosphere forms nitric acid which is a component of some acid rains. The nitric acid is then absorbed by the plant leaves and/or roots. The carbon needed by plants is obtained in the form of carbon dioxide from the atmosphere whereby plants release the oxygen from the carbon dioxide in the process of photosynthesis. Also, when soils contain organic matter in the form of humus, the plant roots can assimilate the carbon from the humus.

What about the carbon contained in organic matter in the soil?

The organic matter in soils decomposes under the action of friendly aerobic soil bacteria which then give off carbon dioxide to the atmosphere, or friendly anaerobic bacteria which give off methane, commonly called swamp gas or marsh gas. Part of the organic material in the soil in the form of humus is absorbed by the plant roots.

Does all the organic matter in soil decompose?

No. Part of it is buried and forms the basis for future fossil fuel deposits. Part of it is dissolved in the soil water and is leached down to the water table where it becomes a natural component of ground water in aquifers.

What other benefits does rock dust provide for soils?

Rock dust increases the moisture holding capacity of the soil, thereby making plants more resistant to droughts.

How does it do that?

1) The fine particles of rock dust hold water more readily by capillary attraction than the coarse particles found in many soils, especially sandy soils.

2) Rock dust promotes the growth of soil bacteria (which are composed mostly of water) and other soil organisms that contain water. The organisms don't drain out of the soil as easily as clean water.

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Are there any less obvious benefits to using rock dust in soils?

Yes! Absolutely! Rock dust helps: 1) combat global warming and the greenhouse effect, 2) remove pollution from the atmosphere, and 3) protect the ozone layer.

How in the world does rock dust do all that stuff?

By absorbing carbon dioxide and helping plants grow healthier and larger.

Wait a minute! I know that when plants grow they absorb carbon dioxide from the atmosphere and store it in the form of organic matter in trees and roots which some scientists believe helps combat the carbon dioxide induced greenhouse warming effect. How does rock dust by itself absorb carbon dioxide?

This is a little bit complicated. The rock dust contains calcium and magnesium locked up in the form of silicate minerals. When the silicate minerals decompose (geologists and soil scientists call the process weathering), the calcium and magnesium atoms which are released combine with carbon dioxide from the atmosphere to form limestone and dolomite which are deposited in the earth or in the oceans.

Does that mean that if we added enough rock dust to the soils world wide, we could prevent the atmospheric carbon dioxide content from increasing and thereby combat global warming and the greenhouse effect?

Yes, that is correct.

How much rock dust would have to be added to the soil world wide to stabilize the atmospheric carbon dioxide content?

About 3 tons per acre per year, assuming that:

1) fossil fuel use continues at the 1994 rate, and

2) destruction of forest lands world wide is halted.

Does this calculation include the factor of trees growing faster (whereby the trees themselves absorb extra carbon dioxide) when rock dust is added to soils?

No. Most trees grow much faster, some as much as four times faster when rock dust is added to soils. To stabilize the atmospheric carbon dioxide content by rock dusting existing forests and agricultural lands, it would require less than about one ton of rock dust per acre per year. If the world land area devoted to forests is increased, the carbon dioxide content of the atmosphere would be reduced by rock dusting soils even at the 1994 rates of fossil fuel consumption.

Let's see if I have this straight now. When rock dust is added to soils, it promotes removal of carbon dioxide from the atmosphere in two ways: 1) by decomposing and then forming limestone deposits deep in the Earth and in the oceans, and 2) by helping trees and all plants grow faster and bigger so that the plants absorb carbon dioxide faster and store it in the form of organic matter, as living plants or organic debris buried in sediments?

Yes, that is correct.

You say the atmospheric carbon dioxide content can be stabilized simply by adding rock dust to the soil world wide. That sounds a lot like pie in the sky to me! Where would the money come from to rock dust the entire Earth?

Using rock dust for agricultural purposes does not cost money. IT MAKES MONEY! The following figures are eye openers and are typical. The Harding Brothers Banana Plantation in Innisfail, Australia conducted a four year test using rock dust. The banana plantation used rock dust (a local Australian brand named Min Plus) at the rate of 2.81 tonne/hectare (1.25 ton/acre) per year at a cost of $125 per tonne ($113 per ton). There was less banana damage from wind, nematodes, insects and disease in the bananas grown on rock dusted soil. (About 20% crop loss with normal agricultural practice but only 5% crop loss when rock dust was used.) When using rock dust, the banana plantation needed less urea, potash and dolomite fertilizers, thereby saving on fertilizer costs at the rate of $3547 per hectare per year ($1435 per acre per year). With using rock dust, the banana crop yield increased by 80%. The total cost benefit of using rock dust was $56,722 per hectare per year. Economists please take note of this case study. The investment in rock dust was $351 per hectare per year, which yielded a return on investment of $56,722 per hectare per year. This is a return on investment of 16,160%. Yes, that is correct, sixteen thousand percent return on investment!

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How does rock dusting soils remove pollution from the atmosphere?

Trees naturally remove from the air such pollutants as carbon monoxide, sulfur dioxide, nitrous oxides, PCBs, DDT, Freon, unburned hydrocarbons resulting from auto engine exhaust emissions and ozone contained in smog. Rock dusting soils helps trees grow better and faster, thereby helping the trees to remove air pollutants faster.

How does rock dusting soils help protect the stratospheric ozone layer?

The public is generally aware that many scientists believe that chlorofluorocarbons (CFCs) [various brands of Freon] used in refrigerators, air conditioners, spray cans and fire extinguishers migrate upward and destroy ozone in the stratosphere. So far, no known natural processes in the lower atmosphere prevent the CFCs from reaching the stratosphere. However, it was discovered that trees absorb Freon and DDT but release them into the atmosphere during forest fires. There are other chemicals produced in massive quantities (both naturally and artificially) which deplete the stratospheric ozone layer such as nitrous oxide, methyl bromide and methyl chloride. These chemicals are produced by natural and man-made forest fires. Burning of fossil fuels produces nitrous oxides. Fortunately, trees remove part of the nitrous oxides and methyl chloride from the lower atmosphere before they drift up to the stratosphere. Trees which are made healthier by rock dusting the soils remove these ozone depleting chemicals more rapidly, thereby reducing the amount of pollution that eventually makes it up to the stratosphere.

Why do we need to protect the stratospheric ozone layer?

To keep ultraviolet light from reaching the land surface.

Why do we want to keep ultraviolet light from reaching the land surface?

Several reasons:

1) Ultraviolet light is toxic to all living things. It interferes with the photosynthesis process such that plants, which we all need, do not grow as well as they should.

2) Even though ultraviolet light is used to treat some skin ailments, medical doctors tell us that excess ultraviolet light is believed to be a factor in causing skin cancer.

3) The extra solar energy which penetrates to the land surface and into the oceans can cause additional global warming.

4) The extra solar energy which reaches glaciers in the form of ultraviolet light could penetrate into the ice and promote melting of the ice, thereby causing the sea level to rise more rapidly than it is rising at the present time.

How does rock dusting soils help fight global warming?

A major factor causing global warming is destruction of trees (tree loss removes the evaporative cooling effect of trees) which are replaced by asphalt highways, parking lots, buildings and other impermeable surfaces, as well as grass lawns and agricultural lands. You can demonstrate this for yourself by standing in the middle of an unshaded parking lot in the summer time. Notice that the asphalt and air are very hot, but if you go stand under a nearby shade tree, the air and ground are cooler. The graph in Figure 4 shows soil temperature measurements made by the author in Piscataway, NJ which demonstrate that replacing trees by grass and/or asphalt causes environmental warming. Trees cool the environment by evaporating much water. When trees are removed, the evaporative cooling effect is removed. When soils are rock dusted, trees (and other vegetation) grow faster and evaporate more water, thereby cooling off the atmosphere faster.

Couldn't we just plant more trees everywhere, including trees in urban areas so that the trees shade the streets, parking lots and buildings to increase the cooling effect of trees on the environment?

Absolutely! But rock dusting soils makes all trees and vegetation grow faster. It takes many years for a tree to grow up to become a significant absorber of carbon dioxide and a significant evaporator of water, but the beneficial effects of rock dust start virtually immediately.

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What about limestone? Isn't that good enough by itself to add to the soil without going to the trouble of adding rock dust?

No, for several reasons:

1) Limestone does not contain significant quantities of all of the trace elements needed by vegetation which are found in rock dust.

2) Using limestone does not remove carbon dioxide from the atmosphere since it already contains carbon dioxide in the form of calcium carbonate and magnesium carbonate, whereas rock dust made from silicate rocks absorbs atmospheric carbon dioxide when the rock dust decomposes in the soil. Adding lime by itself helps to offset the harmful effects of acid rain. If you are already using lime, continue to do so. A good strategy is to mix some rock dust with your lime when you spread the lime on your lawn or fields.

Isn't adding compost or manure to the soil the best way to build up the soil and increase agricultural productivity?

That depends on the quality of the compost. Just as different vegetables contain different mineral contents, the mineral content of compost varies depending on the type of organic material used to make the compost. For example, recall that spinach is noted for having a very high iron content compared to most other vegetables. Organic matter when added to the soil tends to make the soil acidic unless the organic matter contains sufficient calcium and magnesium which tend to neutralize the acids formed by the decaying organic matter. The calcium and magnesium can be added in the form of rock dust or pulverized limestone. A study conducted at the University of Maine's Wolfe's Neck Farm, Freeport, ME, compared the yield of 1st hay cutting using different types of organic matter (See the chart in Figure 2). All four types of material (N-Viro Aglime, Manure-Newspaper, Manure-Sawdust, and South Portland Compost) contained organic material, the last three being mostly organic material. However, the N-Viro Aglime contains 1) calcium which neutralizes the acids formed by acid rain and the organic material in the N-Viro Aglime and 2) cement kiln derived trace elements which encourage soil bacteria growth. Adding rock dust to animal feed increases the trace mineral content of manure and improves the quality of manure. Mixing some rock dust with organic matter, which is used for composting, speeds up the composting process and improves the quality of the compost.

Where can we get rock dust?

You can obtain rock dust in bulk from most gravel pits and rock quarries. You can obtain rock dust in small quantities by mail order or from some local dealers. The Starduster Foundation, c/o Donald J. Supkow, 28 Sefton Circle, Piscataway, NJ 08854 will ship a 3 or 50 pound sample of rock dust anywhere in the continental USA. Call (732) 752-3189 for costs and types of rock dust available.

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How much rock dust would I need to improve my soil?

That depends on the condition of your soil and type of plants. Organic Gardening magazine recommends about 3 to 20 tons per acre (about 15 to 90 pounds per 100 square feet). It also depends on how fine the rock dust is. In general, the finer the rock dust, the less your soil needs for maximum benefit. Much of the rock dust available in bulk form from quarries contains significant quantities of grit and sand sized particles along with the dust. The larger sized particles are not as beneficial to the soil because they have less surface area for soil bacteria to work on. The best way to find out what your soil needs, if you are really serious about improving your soil, is to have a soil test made which tests for assimilative mineral content.

Whoa! What's this about assimilative mineral content? Isn't the mineral content of the soil just ordinary mineral content?

Absolutely not! Let's take a very simple analogy. Suppose you were on a desert island with truck loads of canned food. The food would not be of any benefit to you unless you had a can opener or some other means of opening the cans so that you could get the food out of the cans. Likewise, when the minerals are locked up in large grains of sand in the soil, the minerals are not easily assimilated by the plants. The minerals are more easily assimilated when they are in organic form. The soil bacteria can convert the minerals to organic form (such as humus) when the soil grains are very fine, preferably finer than 200 mesh.

Where can I have an assimilative soil test performed?

Send your 1 pound dried soil sample and your check for $28.00 to A&L Plains Laboratories, 302 34th Street, Lubbock Texas 79408 Ask for the FERTIMAX II soil test.

How much does rock dust cost?

Rock dust is literally dirt cheap! Some quarries will let you have it for about $2 to $3 per ton by the truck load. Some quarries may give it away free. The cost of hauling is extra, so try to find it locally. It may cost $6 to $10 per ton including transportation.

Wait a minute! I live in an apartment and I can't use a truck load of rock dust! How much rock dust would I use for my potted house plants?

Try using about two or three tablespoons full for each potted plant. If your rock dust contains sand and grit, you will need more.

How long does the rock dust last in the soil?

Several years, depending on the soil conditions and the type of vegetation growing in the soil.

Why does it last so long?

The rock dust is not water soluble, so it is not easily leached away by rain. The rock dust breaks down slowly under the action of soil bacteria and plant roots.

Is there any difference in the quality of rock dust as far as the mineral content is concerned?

Yes. Tests by researchers of various types of rock dust show that some rock dusts perform a little bit better than others. However, tests showed that soils with different types of rock dust all performed much better than soils having no rock dust.

What kind of rock dust is Planters II?

Planters II is mostly gypsum which contains too many impurities, such as organic matter, to be used for making gypsum wall board commonly known as sheet rock.

What kind of rock dust is Min Plus?

Pulverized basalt that is mined in Australia (Basalt is also known locally in the USA as trap rock.)

What kind of rock dust is Clod Buster and Fertimax?

Clod Buster is geologically concentrated humus which is mined in New Mexico. It contains about 15% humus. The material contains about 45% organic compounds which include carbon and various trace elements combined with carbon.

Fertimax is Clod Buster which has various specific elements added to it, based on a soil test, designed to bring the soil into optimum balance in a specific location for agricultural use.

So, rock dust made from granite, basalt or mixed gravel provides all the trace elements plants need, but with a shotgun approach in regard to the quantity of various trace elements present compared to what the plants need?

That is one way of putting it. With common rock dusts made from silicate rocks, the plants pick and choose what they need. Some time is required for the soil bacteria to convert the elements into an assimilative form which the plants can utilize. With Fertimax, the mixture of elements is formulated based on what is missing from the soil and the mixture is then put into an assimilative organic form by a proprietary process.

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Can rock dust help keep bugs and insects away from my plants?

Yes, according to Organic Gardening magazine and Remineralize the Earth magazine.

How does it do that?

Several ways:

1) When rock dust is added to the soil, plants receive all the trace elements they need to be healthy and strong. When the plants are healthy, they have a natural immunity to insects and diseases.

2) By dusting rock dust directly on your plants, this seems to keep away the bugs that like to chew on and eat your plants. The bugs don't seem to enjoy chewing on the hard particles of rock dust.

3) Sam Catalano, a sugar cane plantation owner in North Queensland, Australia, claims rock dust keeps away the insects that like to eat sugar cane. At the "Soil Remineralization and Sustainable Agriculture" forum held in Beltsville, MD on May 24, 1994, Sam Catalano showed photomicrographs of insects (the kind that like to eat sugar cane) before and after they got in the way of the rock dust that was applied to the sugar cane. The hard, sharp particles of rock dust broke off the insects' antennae and hairs, got into their exoskeleton joints, and caused havoc to the insects.

4) Spreading a trail of rock dust around your garden can help keep out slugs, according to Remineralize the Earth magazine editor, Joanna Campe. Some people also use diatomaceous earth (the white powder used in some swimming pool filters) for this purpose. (Diatomaceous earth can be obtained from most swimming pool supply houses. Some dealers may just call it filter media).

Does this mean that rock dust is non-toxic but keeps some bugs away simply because they don't like to eat it?

That is correct. Rock dust is non-toxic to humans, as shown by the fact that some people even eat the stuff, and they are among the healthiest, most long-lived people in the world. But for heavens sake, please don't snort the rock dust! Always use a dust mask when you are applying rock dust, lime, or working in any dusty environment!

Who eats rock dust?

The Hunzas of northern Pakistan, as described in Secrets of the Soil. They drink the melt water from glaciers which is milky in color because it contains so much finely pulverized granite which is pulverized by the slow movement of the glaciers in the mountains. They also irrigate their crops with water containing rock dust.

Could I benefit from eating some rock dust?

Perhaps. Some vitamin and mineral supplements sold in health food stores contain various types of rock dust to provide the trace element content. Rock dust is given to animals as a feed supplement and it makes the animals more healthy and productive, but I am not a medical doctor so I don't recommend that anyone eat rock dust. Most rock dust is intended to be food for plants, not food for humans. You may be better off feeding the rock dust to your plants and then eating the vegetables that they produce for you. This is what Julius Hensel recommended over 100 years ago (1894) in his classic book, Bread from Stones.

Does that mean that the plants adsorb minerals like calcium, iron, copper, etc. from the rock dust and we get the extra minerals when we eat the plants?

That is correct. The chart in Figure 3 shows the results of a field test that was performed on the Bob Love organic farm in Minnesota by Dr. David H. Miller, Professor of Biology at Oberlin College in Ohio. Bob Love raised two fields of carrots, one with rock dust and one without rock dust. The rock dust was made from gravel dredged from the Mississippi river. Notice that the mineral content of the carrots was significantly greater in the carrots grown with rock dust than it was in the carrots grown without rock dust.

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What does good rock dust look like?

Fine rock dust looks something like talcum powder. You can obtain a 3 or 50 pound sample of very fine (minus 400 mesh) rock dust from the Starduster Foundation, 28 Sefton Circle, Piscataway, NJ 08854. Call (732) 752-3189 to obtain costs. You can use it as a sample to show a rock quarry owner what you are looking for if you need rock dust by the truck load.

Try it! You'll like it!

Here is a very recent question and answer pertaining to rock dust:

The trace elements that occur in various types of volcanic rock are generally similar to each other in terms of chemical composition. The main difference is in the concentration of each individual element which may vary from one type of volcanic rock to another. The concentration of a particular element, say magnesium, may even vary in a certain rock type such as basalt, depending on which quarry it came from and even from which layer it came from within a particular quarry. When lava flows cool, some heavy minerals such as olivine, settle out to the bottom of the layer. The famous cliff called the Palisades of the Hudson on the New Jersey side of the Hudson River, is an igneous rock intrusion which never escaped to the land surface while it was cooling. It contains an olivine rich layer at the bottom contact with the underlying shale. Thus elements contained in the olivine crystals are enriched at the bottom of this rock layer while these same elements are somewhat less concentrated in the upper part of the layer. The main thing to consider is that most igneous or volcanic rocks contain all of the trace elements found in the chemist's Periodic Table of Elements. When plants grow, they pick and choose what elements they need from any rock dust which is added to the soil. The most important factor in rock dust is the degree of fineness of the rock dust. The finer the rock dust is, the more easily soil bacteria decompose the dust particles and release the trace elements contained with them, putting the trace elements into a form which the plant roots can absorb. The type of igneous rock that the rock dust comes from is only of secondary importance compared to the fineness of the rock dust. If you read the carrot study done at the John Love organic farm in Minnesota, you will notice that the rock dust used in the experiment was simply made from gravel that had been dredged up from the Mississippi River. This gravel was probably composed primarily of granite pebbles. I hope this answers your question.

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Chapter Titles



by Frederick I. Scott, Jr.





Chapter 8 ORGANIC vs. COMMERCIAL FOOD: The Rock Dust Connection





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