A detergent composition containing an inexpensive detergent builder in the form of a selected crystalline calcium carbonate is provided. Specifically, the crystalline calcium carbonate has a substantially rhombohedral crystal structure with null1,0,-1,1null crystallographic indices. The crystalline calcium carbonate can be calcite that has been specially modified to a rhombohedral crystal structure with null1,0,-1,1null indices. The crystalline calcium carbonate of the present invention is extremely inexpensive because it can be readily formed from inexpensive naturally occurring calcite, and it performs well even when used at large median particle sizes.