Introduction Features Igneous rocks Sedimentary rocks Metamorphic rocks. Introduction Features Igneous rocks Sedimentary rocks Metamorphic rocks Gneiss Gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. Thankfully, he was kidding. Geologically speaking, granite and gneiss are similar, so lumping them together is a reasonable thing to do.
In simplified terms, you can think of gneiss as a metamorphic version of granite. Both gneiss and granite are made of feldspars, quartz, mica, and smaller amounts of dark colored minerals like hornblende. Both have tightly interlocking minerals, so they are minimally porous.
On paper, they have similar properties and can be used in the same ways. The difference between granite and gneiss is in their overall texture and movement. Granite is evenly speckled. It formed from liquid magma that cooled and crystallized. Granite is like rocky road ice cream — a solidified conglomeration of different ingredients. Viscount White. Photo courtesy of Arizona Tile.
Gneiss, arguably, is more visually interesting. The stone captures the expressiveness and movement that come from its dynamic origins. The striped, wavy look of gneiss comes from extreme amounts of compression.
The random orientation of minerals you see in granite is an inefficient use of space, sort of like the ragtag pile of magazines you left next to the couch. Those magazines take up less space if you stack them all the same way, right? The appearance of granular minerals is what marks the transition into gneiss. Intense heat and pressure can also metamorphose granite into a banded rock known as "granite gneiss.
Folded Gneiss: A photograph of polished gneiss from the stock of a countertop vendor. The view shown in the photo is about 12 inches across. Numerous tight folds are visible in this rock. Click to enlarge. Although gneiss is not defined by its composition, most specimens have bands of feldspar and quartz grains in an interlocking texture.
These bands are usually light in color and alternate with bands of darker-colored minerals with platy or elongate habits.
The dark minerals sometimes exhibit an orientation determined by the pressures of metamorphism. Some specimens of gneiss contain distinctive minerals characteristic of the metamorphic environment.
These minerals might include biotite , cordierite , sillimanite, kyanite , staurolite , andalusite , and garnet. Gneiss is sometimes named for these minerals, examples of which include "garnet gneiss" and "biotite gneiss. Garnet Gneiss: A photograph of polished garnet gneiss from the stock of a countertop vendor.
Gneiss usually does not split along planes of weakness like most other metamorphic rocks. This allows contractors to use gneiss as a crushed stone in road construction, building site preparation, and landscaping projects. Some gneiss is durable enough to perform well as a dimension stone.
These rocks are sawn or sheared into blocks and slabs used in a variety of building, paving, and curbing projects. Some gneiss accepts a bright polish and is attractive enough for use as an architectural stone. This coarse-grained metamorphic rock is sually used for exteriors.
In this article, you will find out everything you always wanted to know about this natural stone. The minerals are arranged into layers that appear as bands in cross section. The darker bands have minerals such as magnesium or iron and lighter bands contain silicate minerals aluminium, sodium, potassium, etc.
Although gneiss and granite have similar properties resistance, hardness, durability , they have different textures and finishes. The foliated texture of this stone combines light and dark minerals. The colors are very variable, generally alternating lighter and darker discontinous bands white, pink or grey. Gneiss can be used for interior and exterior spaces in buildings, walls and landscaping.
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