Here's why:

* Breccia is a rock type, not a specific mineral. It's made up of various fragments of different minerals and rocks cemented together.

* The specific gravity of breccia depends on the composition of the fragments. For example, a breccia made of mostly dense quartz fragments will have a higher specific gravity than one made of lighter limestone fragments.

* Porosity also affects specific gravity. If the breccia is highly porous, it will have a lower specific gravity.

Therefore, to determine the specific gravity of a particular breccia sample, you would need to analyze its composition and porosity.