Quartzite breccia, Rincon Mountains, Tucson, Arizona

&lt;p&gt;This is a fault breccia collected along a high-angle Basin and Range fault in southeastern Arizona. &amp;nbsp;It is monolithologic, i.e., only contains pieces of quartzite. &amp;nbsp;I imagine that this is an implosion breccia, produced when sudden faulting along a curved or irregular part of the fault creates (for a nanosecond) an opening or void (even at great depth), causing the walls of the cavity to implode and attempt to fill the volume. &amp;nbsp;At the same time, mineralizing solutions suddenly ‘feel’ a huge drop in pressure and instantly dump minerals (in this case silica) that had up to then been dissolved in solution. &amp;nbsp;Perfect implosion breccias are marked by an array of angular pieces that can be re-fit together. &amp;nbsp;These kinds of breccias are not produced by grinding or shearing or cataclasis within a fault zone.&lt;/p&gt;

Whereabouts

I collected this in ~1997 along the Martinez fault at the southeastern-most corner of the Rincon Mountains. I like the fact that it comes in the form of a thin slab, almost like a piece of floor tile that you would find at a store.

Age & Formation

Cambrian Bolsa Quartzite formation, ~500 Ma.