Here's why:
* Breccia is a rock type, not a mineral. The Mohs scale measures the hardness of *minerals*.
* The hardness of breccia depends on the minerals it contains. Breccia is formed from broken fragments of other rocks (clasts) that are cemented together. The hardness of the breccia will vary depending on the hardness of the clasts that make it up.
For example:
* A breccia made up of mostly quartz fragments would be harder than a breccia made up of mostly limestone fragments.
To determine the hardness of a specific breccia sample, you'd need to identify the minerals present and consult the Mohs scale for their individual hardness.
