Dolomitic limestone is a type of limestone that includes up to 50 percent dolomite. Normal limestone is primarily made up of calcite and aragonite, but dolomite forms in limestone when the calcium ions in the calcite part of the limestone are replaced by magnesium ions this process is called dolomitization. Dolomitic limestone was once referred to as magnesian limestone in the United States Geological Survey publications, but is now known as dolostone, dolomite rock, dolomite limestone, or dolomitic limestone. Dolomite is a mineral which contains large amounts of calcium and magnesium, which makes it a good fertilizer for nutrient deficient soil.
Usually, agricultural lime is derived from calcitic limestone and lime derived from dolomitic limestone is labeled as such.
But I have seen bags labeled agricultural lime derived from dolomitic limestone. Same with *garden* lime. Usually calcitic, but I've seen dolomite labeled as garden lime. In fact, I have a 40lb bag labeled just that way. They can call it what they like, the ingredient list is what tells the real story.
Either one is fine, dolomitic or calcitic, so don't stress if you can find one but not the other. I have both and use both.