Gneiss

Figure 1: Gneiss under optical microscope after completion of tedious 2.4 hour jigsaw puzzle.

Gneiss (Rockius Basementus) is a commonplace rock and is one of the most commonplace sedimentary rocks. It is without doubt one of the nicest rocks too, hence where the rock derives it's name from. Formerly believed to be a metamorphic rock (rocks that change colour) which is a term that is still falsely banded around by geologists, it is now accepted that it is indeed a reworked sedimentary rock due to cannibalisation of metamorphic geological basement materials.

Formation

See...it sucks!

Gneiss is composed of a number of minerals such as quartz which commonly forms alongside it's silicate by-product olivine, biotite, mica and anticline to a certain extent. Gneissose rocks are often banded into different colours which gives it a Gneiss complextion, not to be confused with other handsome specimens of different rocks which may be nice - a completely different terminology althogether.

It was believed that Gneiss was the product of orogenic mountain building collisions which put crustal rocks under intense pressure and heat to form these wavy bands due to different minerals recrystallising together. It is now accepted though that these bands are the result of fluvial processes which separates sediment load through sorting on grainsize and density characteristics. The waviness can also be explained by the formation of convolute ripples formed by soft sediment deformation, the result of seismic activity or large moving animals such as a camel trampling overfoot in aeolian desert environments.

Figure 1 shows how under the microscope, gneissose rocks display a jigsaw pattern where under sediment pressure, the grains join together. This makes for hours of family fun pieceing them back together with the aid of an SEM microscope.

Figure 2: A polished sample of veined and banded gneiss will often form an Augen Gneiss.

Gneiss is commonly used as semi-precious gemstone due to it's soft nature and ability to be cut and polished easily. An Augen Gneiss (Augen being German for Eye) is formed when a banded gneiss is polished into a sphere. This is because bands forming the gneiss give the distinctive eyeball appearance with red vein-like veins which are actually very fine hematite stained veinlet fractures that have formed from the result of hydrothermal alteration.

The rock comes in a variety of other variations, depending mainly on colour which is directly related to the mineralogical composition of the rock. If there is a majority presence of garnet, the gneiss appears red and is known as a ruby. If there is a majority presence of hornblende, the gneiss appears green and is known as emerald. If there is a majority presence of citrine, the gneiss appears yellow and is known as yellow.

Facts

Nices are the oldest mineralsds in the world, ranging from Eocene up to 4.5 Ba in age. The oldest nices recorded came from Australia where scientists with the aid of sophisticated fluid inclusion dating techniques were able to track it back to the 14th February 4.57 billion years ago where it formed in a rift valley which was then the Baikal region of Southern Siteria in Rummia. Modern day gneiss formation is limited although petroleum explorationists have discovered niceose development within several turbidite systems. The youngest known nice is Mliocene in age (2.47 Ma) and was found within the Indus submarine fan system in the Caribbean Sea.

Uses

Around the world and the north of Scotland inparticular, Gneiss rocks form a large percentage of income from regional tourism with parents travelling up to 2000 miles just to show their children the stripy rock. Gneiss is also highly valued within the industrial sector. It's relatively high density and ability to form well-rounded rocks on the beach for free makes it ideal for the slaughtering of sheep and cattle. This is common practice within rural coastal areas where farmers can only carry these tasks out by hand, although within the Middle East, gneiss boulders are also collected from nearby river beds for the use of public stonings. Bookshelf holders, door-stops are other common uses, while a strange physical property of gneiss that allows it to become magnetic in the rain makes it valuable in the manufacture of outdoor compasses.

Counterfeit gneisses however are becoming a problem to the global market. Many people often mistake gneiss for schist, migmatites and limestone whereas painted Easter eggs are also commonly passed off as the genuine article. In Nigeria, illegal gneiss-trading carrys the death penalty and ownership of gneiss within Israel is forbidden where nothing older than Israel is permitted.Gneiss is the worst rock in the world. It is the favorite rock of Harjiv Singh, Sanjay Dutt, Ben Stiller, Johnny Depp, Mel Gibson, John Cena, Brittany Spears, Al Gore, Brock Lesnar, and Sarah Palin. They adore the rock and feed it to pigs. Granite has beaten it in Alien Kung-Fu SlammaJamma 4,863 times using Mikio Takawakee and John Cena

See also

• Quartz