From
www.sciencedirect.com/topics/medicine-and-dentistry/ammonium-nitrateANFO and emulsion explosives are now the most widely used explosives all over the world. ANFO is composed of approximately 94% AN and 6% fuel oil by weight.
You just need some scales ;-)
From
offroadingpro.com/how-much-does-a-gallon-of-diesel-weigh/ It is important to note that fuel volume fluctuates with humidity, temperature, or weather change. At room temperature, diesel is below 7 lb/gal. At 32°F, it’s a little over 7 lbs. And at very high temperatures of 100°F or above, a gallon of diesel will weigh about 6.8 lbs.
I'd say call it 6.95lb/gallon at room temperature and work with that. You're just looking to break up some rock and it's something you can do again if you don't get it right the first time. Start small - if the rock only cracks a bit, the machines may be able work with that. How big is small? Maybe a 12 gauge shell's worth? I've never used ANFO and I don't have a quick reference other than that FM, which talks about the various military explosive devices such as:
1-10. Forty-Pound, Ammonium-Nitrate Block Demolition Charge
a. Characteristics. Figure 1-5 (page 1-8) shows the 40-pound, ammonium-nitrate block
demolition charge or cratering charge. It is a watertight, cylindrical metal container with
approximately 30 pounds of an ammonium-nitrate-based explosive and 10 pounds of TNT-based
explosive booster in the center, next to the priming tunnels. The two priming tunnels are located
to the outside of the container, midway between the ends. One tunnel serves as a cap well for
priming the charge with an M6 electric or M7 nonelectric military blasting cap. The other tunnel
series as a priming path, with the detonating cord passing through the tunnel and knotted at the end.
There is a cleat between the tunnels to secure the time blasting fuse, electrical firing wire, or
detonating cord. There is a metal ring on the top of the container for lowering the charge into its
hole. Table 1-2 (page 1-5) lists additional characteristics for the 40-pound, ammonium-nitrate block
demolition charge.
1-7
FM 5-250
b. Use. This charge is suitable for cratering and ditching operations. Its primary use is as a
cratering charge, but it also is effective for destroying
buildings, fortifications, and bridge abutments.
c. Advantages. The size and shape of this charge make it ideal for cratering operations. It is
inexpensive to produce compared to other explosives.
d. Limitations. Ammonium nitrate is hydroscopic. When wet, it will not detonate. To ensure
detonation, use metal containers showing no evidence of water damage. Detonate all charges placed
in wet or damp boreholes as soon as possible.
I certainly don't think you need 40lbs but I don't have access to a "How much to take down a one foot tree?" type chart. Just try to keep your eyes and all your fingers - too much of that stuff can be dangerous.
Some further notes from the FM about ANFO :
All military explosives can create antitank craters. When available, use the 40-pound, ammonium-nitrate cratering charge (Figure 1-5, page 1-8) for blasting craters.
Improvised Cratering Charge. This charge consists of a mixture of ammonium nitrate fertilizer (at least 33.33 percent nitrogen) and diesel fuel, motor oil, or gasoline. The ratio of fertilizer and fuel is 25 pounds to 1 quart. The fertilizer must not be damp. You may fabricate almost any size of improvised charge from this mixture. Proceed as follows:
a. Measure the fertilizer and fuel for the size charge you require.
b. Add the fuel to the fertilizer and mix thoroughly.
c. Allow the fuel to soak into the fertilizer for an hour.
d. Place half of the ammonium nitrate charge in the borehole. Then, place two l-pound primed blocks of explosives in the borehole and add the remainder of the ammonium nitrate charge. Never leave the charge in the borehole for a long period, since the charge will accumulate moisture, reducing its effectiveness.
NOTE: Boreholes should receive 10 pounds of explosives for every foot of depth and must be dual primed.
e. Detonate the charge.
I think that last note works out to less than a pound for each inch of material. That's for blowing everything away (cratering) so probably much less to just break the rock. Remember, you just want to make it movable in pieces, not have flying debris.
Make a small charge and detonate it on hard ground and see how much damage it does. Then adjust the size to do what you need done. You might consider packing dirt on top of the charge so most of the explosive force goes into the rock and not out the bore hole. Save the tamping for the second in-the-rock charge, if needed.
Again, be careful.