Chuck,
I guess you saw where that gent was asking about breccias. I trust he found his way to Wikipedia. They even have pictures he can use in the talk he’s going to give. He was talking about rocks he’d seen at an impact structure and here we talk about micro stuff but the definition is the same. This is from Wiki (they say the word is from Italian). Breccia is a rock composed of angular fragments of minerals or rocks in a matrix (cementing material), that may be similar or different in composition to the fragments. Well put. How about some pictures?
– John
The surface of the moon has fragments, it’s really been pounded. This slice is 20 mm long, about
three quarters of an inch, and is a breccia. It is NWA 2727, a lunar olivine gabbro with mare basalt clasts.
This is the top part of that slice in thin section viewed in cross polarized light.
Impacts on the moon both break up the surface and weld it together. Then break it up some more. DaG 400 is a product of that process and has been called a breccia in breccia. The sample on this thin section is about the same size as the slice above. Here we see it in reflected light. It takes some study to pick out the different clasts.
Same slide in XPL.
A 2.6 gram slice of a eucrite plutonic breccia, NWA 3159.
A thin section of the same meteorite. The orange rectangle marks the area shown below, magnified and in XPL.
NWA 3159 Eucrite Plutonic Breccia XPL FOV 3 mm.
My favorite on this page – a lunar feldspathic breccia, NWA 2995.
Bilanga is a diogenitic breccia. Some mineral grains got broken and ground smaller and smaller, “comminuted”.
