Rock

[tfb37]

Howard has mentioned decomposed granite several times. My tired old mind can't get around the concept of granite decomposing. What the heck is it? Please explain.
Thanks

[Dchall_San_Antonio]

I'm not sure I can explain it. The granite you see around here is usually solid rock suitable for cutting and polishing. Decomposed granite is a fragile material. If you could find a fist sized rock of decomposed granite and you threw it hard to a concrete surface, you would have a pile of granite flakes about the size of aquarium sand. It's like the granite has been acted upon by an acid for a few thousand years and the "fault lines" have been weakened.

I grew up in Southern California in a hilly area where decomposed granite was the basis for every hill. When homes finally went up on these hills, they simply scraped off the surface and put in houses. The neighborhoods were solid but if you wanted to plant grass, or God forbid, a TREE, you were screwed. Digging was possible with a pick but not really very practical without heavy equipment. Trees were just stunted in small holes for their entire lives.

[Tricky Grama]

Ok, I have a probably dumb question: we have a crushed granite drive way on our acreage, will this eventually decompose? Or not for humdreds of yrs? Or is this a different type of granite that's used for driveways?
Patty

[CaptainCompostAL]

My understand is that more and more soil scientists are discovering the power of rock powders in relation to soil building and building the health of all soil organisms.

All rock powders are great sources of minerals and micronutrients. All animal forms need minerals. As the microbes and macrobes like earthworms, digest the insoluble minerals, they break down into the various soluble micronutrients that all forms of plants need.

For example, limestone rocks are rich in calcium. Granite rocks are rich in potassium, etc. Seaweeds of course are the king of micronutrient fertilizers and soil amendments. There can be up to 70+ trace elements in seaweed.

For larger farms, or for farming systems where seaweed is not readily available in mass, rock powders is one answer to the problem. I have access to truck loads of free rock powders (called "fines"), here at a local limestone quarry here in central Alabama, if I ever needed it for my farm.

It is amazing how more and more research is proving that insoluble tiny particles like rock powder minerals, can be easily digested or absorbed via microbial activity, over time, into the anatomy of growing plants, thriving in the presence of rich organic compost, and other forms of powerful biostimulants like aerobic compost teas, or etc.

Happy Gardening!

[Dchall_San_Antonio]

pjva,
Can't tell from here. If it holds a sharp edge without chipping when struck with the back of a knife, then it should last a few million years. If you can easily flake off parts, then it might be decomposed.