NP
Silence - never be sorry for questions you've asked.
You are looking for the larger "sand" sized Calcium Carbonate. I've seen it in two different sizes locally - one is pretty chunky (like the brown cement sand Quikrete sells), and is what I prefer, the other is sugar fine, like what we would use in our tank for the DSB. You have to be careful though, and make sure you get Calcium/limestone based grit and not the Granite (or other?) based grit.
Did they try to sell you
Sodium Chloride or
Calcium Chloride? Neither is what you were looking for in this instance - SC is Salt like table salt, CC is also a salt, but is used to speed the initial set of cement (and to de-ice driveways) - I use this in my personal mix so I can handle pieces earlier (and I think it
slightly speeds the cure as well), but it isn't something you would use as an aggregate.
You might also look at your local big box stores - Pulverized Limestone or Limestone Sand are pretty much all the same thing.
And I had a gent from the UK PM me the other day, and he had found something called "Recycled Crushed Glass" - a very intriguing idea - recycling glass into sand. I've not seen this stuff around, but maybe someone else has? I'd be interested in a bag just to see what it is like, if for nothing else, but this might also be an idea for a sand aggregate. So if anyone spots any, get me the name of the chain and a SKU if possible. Thanks!
And as far as steaming the rock goes, please reconsider using the "high heat" variation.
There is a pretty good chance that baked rock will develop problems down the road, and even though I've made no bones about the potential problems this method could cause, I'd still feel bad if people came back with a bunch of failed rock, especially when I think I've found a better way to do it. Now if you are just curious, or making sump rock, then that is ok, but if things go as planned tomorrow, I will do a write-up of the "low heat" method, which should produce much stabler rock. In fact, I've emailed "JohnL", the mod, to see about having the old method post deleted so there won't be the potential for people to get confused.
It sounds like you have a pretty firm grip on the procedure, however, the vinegar bath is 1/4cup per gallon of water, not 10%. I would NOT wrap the piece in tinfoil, but line the bottom of the oven with it, as well as "cap" the vent under the top rear burner with foil. I'm sorry, but this
will require you to clean the oven when you are done or your mom is gonna kill you. No matter how careful you are, you are going to get sand in the oven and the steam will lift any grime that is in the oven and get sort of icky.
And I would imagine that the fumes are not great for birds, but it didn't seem to bother the cats, dogs, people or tanks - birds are so sensitive to stuff like that, I'd be really, really careful. Block off all the vents to that room, and block off the kitchen with a sheet or blanket to keep the fumes contained, and run the hood fan, and if it is warm enough, put a fan in the kitchen window, venting outward.
I've been pimping the chicken grit for like the last 6 months,
Customcolor 
I don't know enough chemistry to know if aluminum oxide would cause a problem. It could be that this would create a "High Alumina Content" cement and be awesome - aluminum powder can create an air entrained effect and create voids, but too much alumina can be poisonous. So it might be bad. I don't know. Maybe someone else can offer their opinion. What % was the Al2O3? What was the bulk of the content? Are you sure that this stuff was for feeding chickens? You could always go to a different feed store and see what they have (or call)...