Hi,
here in Australia there is a new product on the market, brought out by a fertiliser company, which is implying the product is rock dust. It isn't but what that has me now wondering is if the product I am using is a good rock dust. Can some one please give me advice.

thanks in advance

I can tell you that the winemakers along the Ring of Fire that goes up the West Coast, and around the world, absolutely love volcanic soil.  Basalt is one of the types of rocks that is left over from volcanic activity.  It adds great flavor to wine.  It's expensive, though.  I've looked into just shoveling it around perennials, but I can't find sand or powder so I've given that up.

I use granite sand, which is more accessible to plant roots than rock -- rock would take a glacier running over it to make it available to plant roots.  Granite sand has a 10-year source of potassium, and I've shoveled truckloads of it onto my acre garden.   So rock powder, which is finely ground and easily accessible to roots is a good thing. 

If you want to spend the money to use that rock powder, it would take a least a couple of shovels full on a mature fruit tree, or a shovel full on a berry plant to maybe make a difference in flavor of fruits and vegetables, maybe slightly.  You know how they are about describing wines.   

I think adding hundreds of pounds of compost will improve your soil more than rock powder, unless you have a cheap source of it.  Otherwise, granite sand is a really cheap and long-term amendment.

Here's an analysis of Basalt that you can compare.  I see there's uranium in your dust and in basalt...not sure what to think about that.  Was there more in the Fukushima?  They are starting to find atomic particles in Napa wine now, so that atomic leak is showing up.  They say it's below levels that anyone should be concerned about.

https://crustal.usgs.gov/geochemical_reference_standards/basaltbcr2.html

If you can get volcanic lava dust, use it, it is the base of almost all the best soil on the planet.

Don't worry about Uranium unless there is a  high concentration it can be considered normal (our plants are hit by quite a lot of radiation every day (UV a,b&c, gamma, and many protons (that's is what we call sunlight)).

The best rock dust, for minerals is volcanic (igneous) rock the next would be granite (slowly cooled volcanic rock), the last on the list would be from sandstones (sedimentary rocks).

Redhawk

Besides the supplier telling you it is volcanic rock dust how can one tell? For that matter how can you tell which rock e.g basalt, granite igneous, the dust has originated from?
Or am I getting too deep??
thanks

To be certain requires chemical testing for mineral content. Igneous covers all forms of magma rocks (it roughly means fire formed).
Basalt cools slowly but not as slowly as granites, both basalt and granite cool sub surface and this allows crystals to form within the cooling rock.
Pumice is flash cooled and what we know as "lava rock" is magma that reaches the surface and forms lava flows, these cool faster than either basalt or granite.

The easiest way to know for certain would be to grind your own rock dust from lava rocks you gathered.
Most of the lava dust will be from surface cooled magma, like you can find in Hawaii or some places in the lower 48 states like Arizona and New Mexico. 

This topic came about due to discussions in a local network about rock dusts and from what I could debunk easily went on to a much deeper discussion about Rock Dusts with questions raised about using crusher dust instead and how much cheaper it would be. Now I knew from reading most of Dr Redhawks written words on here that it was not right hence the questions. What I have discovered is this - the attachment shows the different rocks the one on the right is where volcanic rock dust comes from the one on the left is what crushed rock/ crusher dust MAYBE made out of because you have no idea what is actually in crusher dust.
You will be lucky to get 20% of the crusher dust to sift at a minus #200-mesh screen, which is the requirement for rock dust. This means that less than 20% of the product you have purchased is available to be used, the rest needs more work.
Anyway I am now happy I am able to be fairly certain the product I purchase is Volcanic rock Dust simply by looking at it and feeling it as it must be the consistency of flour.
Thanks to all who helped.

Judy, don't be afraid to use "dust" that doesn't mesh out, once you add fungi and compost the microorganisms will literally dissolve those larger pieces by excreting enzymes so they can use those minerals.
The larger hunks also give soil more hide places for organisms and help with soil texture, water infiltration and give mycelium places to hang onto and all this only creates a better environment for your plants to grow in.

I like to use the 1 inch or 2.5cm rule, any rock larger can be removed if you want to, but all that are 1 inch (2.5cm) and smaller you definitely want to leave in place.

Vesicular Basalt is called "Lava Rock" in the US, it can be a wide variety of colors from deep black to brick red and even dark tan specimens can be found in some lava flows.
This type of basalt is harder than the fine grained Basalt that is usually found in columns, the grain difference is from the rate of cooling. The holes in Vesicular Basalt come from the bubbles of gas that didn't have time to work their way out before the magma solidified.

Judy,

I use exclusively rock dust from a couple quarries. The price point doesn't even compare, usually it is <$20USD per ton. I am fortunate to have granite and basalt in my area, but the basalt is more expensive for delivery as it is about an hour away. Mostly I use granite, since I have a friend with a small dump truck. I suspect as Bryant has mentioned that the microorganisms in the soil are adept at obtaining the minerals and sharing the wealth, so I am concentrating on maintaining the soil life as opposed to simply trying to make Hawaiian soil in Virginia. Additionally, the larger (still smaller than a pea) particles are useful for ground birds, and that also helps break them down- serving two purposes!

Based on the good Dr Redhawk's advice, recapitulating nature is almost never a bad idea. Adding aggregate that used to be prevalent (it is our bedrock now covered in silt and clay over millenia) seems like a  nice way to rejuvenate the soils at a modest price point.