Have you ever seen this rock?

Our rock of the month’s called Gneiss, a type of metamorphic rock that forms at high depths where pressure and temperature is very high, generating deformation and recrystallization in the minerals, placing them in a preferred direction. This is called the banding and it is for this reason that the colors are different. For definition a gneiss is a metamorphic rock formed in a regional medium-high metamorphism process [regional metamorphism is one that is associated with areas at convergent plate boundaries as subduction zones and mountain formation] of sedimentary rocks and igneous rocks. This alteration increased the size of the mineral grains and segregated them into bands, a transformation which made the rock and its minerals more stable in their metamorphic environment. It is characterized by alternating light and dark bands differing in mineral composition, the lighter bands contain mostly quartz and feldspar, the darker often contain biotite, hornblende, garnet or graphite.
Gneiss rock example
Gneiss rock

The following graph shows the temperature and depth relationship with formation of Gneiss and other metamorphic rocks.

metarockgraph

Gneiss can form in several different ways and it can been classified in orthogneiss and paragneiss. The protolith of paragneiss is a sedimentary rock, by regional metamorphism can transform shale into slate, then phyllite, then schist, and finally into gneiss. During this transformation, clay particles in shale transform into micas and increase in size. Finally, the micas begin to recrystallize into granular minerals. The appearance of granular minerals is what marks the transition into gneiss. And orthogneiss is formed by the metamorphism of igneous rocks. In the next graph shows the relationship of the tectonic environment of the metamorphic rocks with the temperature and pressure

Gneiss usually does not split along planes of weakness, This allows contractors to use gneiss as a crushed stone in road construction and building site preparation, also is attractive enough for use as an architectural stone. Beautiful floor tiles, stair treads, window sills, countertops, and cemetery monuments are often made from polished gneiss.

Gneiss-Dark

Do you know where the oldest rock on the planet is?

The oldest rock on the planet is located in Canada, in the Northwest Territories and is geologically located in the Slave Craton. They have a composition close to granitic and are interpreted by radiometric measurements with ages about 4.03 million years. This is a number that is difficult to comprehend to human scale. This metamorphic complex is located in Archean age moreover this gneiss it’s the most ancient quartz rocks which still exist on the constantly changing Earth’s surface.

canrock
canmap

Canada has very interesting geological regions, for example Mount Head where geology has undergone different geological processes and today different deformational structures are exposed. This area was modeled in the plataform Geomodelr where was shown the relationship between the structures and the disposition of the older rocks with the younger rocks.

geomodelr1mounthead
gemodelrmounthead map2
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