How do I make rock dust?

Question

I have some used fireplace bricks, so I was wondering how can I convert it to rock dust for my garden nutritional value.

To get rock dust, start with rocks - or go buy a bag of granite meal/dust. — Ecnerwal, May 05 '16 at 13:56
Not much in brick to make your garden happy: https://en.wikipedia.org/wiki/Brick#Fired_brick — Wayfaring Stranger, May 05 '16 at 14:09
Fireplace bricks are ideal for building a brick barbecue. Just sayin'. In fact if i was within 100 miles I would take them off your hands... — RedSonja, Nov 28 '16 at 13:25

score 9 · Accepted Answer · answered May 05 '16 at 10:06

9

Rock dust is used in organic gardening where basalt and granite is crushed into a fine powder.

Bricks are made of clay, sand and lime and where

limestone... is often deficient in the majority of essential macro-compounds, trace elements, and micronutrients

Even if you did have access to a commercial rock crusher to crush your bricks they would not add much to your garden. You are better off adding compost or other organic matter to your garden.

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answered May 05 '16 at 10:06

kevinskio

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I would agree. Volcanic soils are known for being "fertile" - it is mainly the potassium but also some phosphate and other lesser ions ("minerals" in horticulture). These are going to be found in the feldspars and lesser minerals in these rocks (granites especially are real grab bags of minerals!). Sand and lime generally do not have any of these - the clays might. Used fireplace bricks might also have some organic nasties? Add compost instead: Less hassle, much more likely to be effective. – winwaed May 05 '16 at 12:50

score 5 · Answer 2 · answered May 05 '16 at 14:07

Crushed fire bricks won't make good rockdust. There just aren't enough minerals present to justify their addition to your medium, or the labor and cost of crushing them into dust.

Contact a quarry or gravel pit, or buy some online. Granite and basalt make the two most nutrient-rich, but with basalt be sure you can look into its composition (there are nutrient-rich basalts, and there are some that are 99% Silicon Dioxide and Aluminum Oxide - essentially inert).

How do I make rock dust?

2 Answers2