Geology And Geophysics

What is Shocked Quartz



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Imagine being lucky enough to find quartz that has qualities that no other quartz has. Quartz is a hard crystal, six sided and formed under enormous increments of time, the perfect conditions and with pressure. It all begins with silicon and oxygen that forms in a tetrahedron, with each oxygen molecule shared by two tetrahedra.

Quartz is a six sided prism that ends with a six sided pyramid at each end. Every time! But quarts does not often have such a perfect shape due to pressures, heat and other factors that may mush it all together or even cause the crystals to grow internally to a rounded shaped container, as with geodes.

Quartz maintains itself until heated to at least 573 degrees centigrade and subjected to at least 1 kilobar of pressure. With more pressure, more heat is required for the quartz to lose stability.

Heat and pressure have contributed to the variety in quartzes, such as citrine, rose quartz, amethyst, and smoky and milky quartz. There is also chalcedony, agate, jasper, tiger's eye, and carnelian.

But quartz has other special qualities, mainly in its ubiquitous nature and in its resistance to weathering in the atmosphere. It is critical to granite and is found in many igneous extrusive rocks, sandstone, shale, sediment and can be in the last tiny bits of fully weathered rock.

Then something happens to create a new form of quartz. This form has planar deformations which can be seen by the naked eye or that are only visible under an optical microscope, usually visible as lines within the quartz crystal. But under an electron microscope, or transmission electron microscopy, more details of the dislocations become available.

The only known forces that have enough power to "shock" quartz are a nuclear explosion, as with the first atomic bomb tests, and the impact of an extraterrestrial object such as an asteroid or meteor. When new meteors hit or when older locations are scouted, this rarest of phenomena is one of the more prized trophies that meteor hunters and scientists hope to find.

Scientists examine the various planar deformations and can deduce the varying amounts of pressure that caused them. After the shock, there is relaxation that occurs and that can even allow new crystals to start growing within the planar boundaries.

The Cretacious Terteriary, or K-T boundary is believed to be from an event where an asteroid of approximately 6 miles in diameter impacted the earth, creating all kinds of havoc, including enough pressure and heat to make shocked quartz. There have been other huge impacts, of course, but the K-T boundary is among the most well known.

Where is shocked quartz found? It has been found at the sites of meteor and asteroid craters and at the sites of underground nuclear tests. One of the most interesting sites where shocked quartz was found is the Hell Creek formation, which is over a thousand miles form the Chicxulub impact crater in Mexico. The Barringer, or Canyon Diable Crater in Arizona is a privately owned site that yielded shocked quartz.

Volcanoes, however, do not produce both the heat and pressure required to make shocked quartz.

The Hell Creek formation has taught that the volume of disruption from asteroid and meteor impacts can distribute ejecta and material around the world, into space, and is suspected of even sending some material into orbit.

As a result, shocked quartz could be found in many places of the world, but finding it is still a rare and difficult accomplishment.


http://en.wikipedia.org/wiki/Quartz

http://www.unb.ca/fredericton/science/emunit/Trepmann/Shocked%20quartz.html


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