FMF - Friends of Minerals Forum, discussion and message board

[Roger Warin]

Hi List,
The notion of shocked quartz cannot be understood as it should be because words sometimes hide concepts.
A shocked quartz is not a crushed rock agglomerated into a breccia. Under high pressures (but limited temperatures) and without destroying their morphology, crystal quartz undergoes a first deformation along the plane (r) (10.1).
This typically occurs in alpine quartz, as shown by my pic of a Disentis quartz.
This quartz crystal then has a fake cleavage along (r), while others remain conchoidal fractures.
But the real shocked quartz are found in impactites, these rocks being impacted by a large meteorite. That is another story.
Roger.

[Pete Richards]

[Bob Carnein]

True "shocked quartz" can be confused with quartz that has undergone metamorphic deformation (Boehm lamellae), and both kinds of features can occur together. Some workers have confused the two. I'd recommend the following article: J.S. Alexopoulos, et. al., 1988, Microscopic lamellar deformation features in quartz: discriminative characteristics of shock-generated varieties: Geology, vol. 16, no. 9, p. 796-799.

[Roger Warin]

Hi List,
Impactites are rocks that have been the target of a large meteorite.
Intense shock obviously disrupts the crystal lattice of mineral grains. When the pressure reaches a field of 5-35 Gigapascals (350000 bars or atm), it may appear in the quartz grains of impactites some "Planar Deformation Features" or PDF's.
PDF's are in fact planar deformation (or acicular grouped in a plane) that appear on many lattice planes. PDF’s aren’t fractures. They are composed of amorphous materials and they can be “decorated”, with bubbles of fluid inclusions.
The least attached plans of their parallel neighbors suffer deformation in the first place. Many other plans (characterized by their different orientation in the crystal) as the most preferred {10.1} are also affected. They were well observed on {01.1} {10.0} {00.1} {11.0} {11.1} {51.1}, etc.. This often gives the appearance of parallel lines that cross the thin blade. These crosses lines are also an identification of PDF's argument, distinguishing polysynthetic twins (repeated multiple times in feldspar or pyroxene).
These rocks are actually the real shocked quartz, a name imposed by scientists studying impact craters.
Roger.