Gneiss
A species of Metamorphic Scientific name : Gneiss RockType : Metamorphic
Gneiss, A species of Metamorphic
Scientific name: Gneiss
RockType: Metamorphic
Description
Physical Properties
Colors
Black, Brown, Pink, Red, White
Texture
Foliated
Chemical Properties
People often ask
General Info
How to Select
Gneiss, a metamorphic rock known for its banded appearance and mineral composition, is valued based on several characteristics:
1.Color and Banding: gneiss with pronounced, contrasting bands of light and dark minerals is often more sought after. The color depends largely on the mineral composition, but varieties with vibrant or unusual colors can be especially desirable.
2.Mineral Composition: The presence of certain minerals can enhance desirability. For instance, gneiss containing garnet or other gem minerals may be considered more valuable.
3.Texture and Quality: A well-formed gneiss with no visible deformities increases the stone's appeal. The degree of metamorphism affects the textural appearance and can influence the value.
4.Size: As with many rocks and minerals, a larger specimen of high-quality gneiss is generally more desirable and valued.
Remember, the most desirable qualities or varieties of gneiss largely depend on its intended use and the preferences of the individual user or buyer.
Usage
Composition
Gneissic rocks are usually medium- to coarse-foliated; they are largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, and so forth. Gneiss rocks may also be named after a characteristic component such as garnet gneiss, biotite gneiss, albite gneiss, and so forth. Orthogneiss designates a gneiss derived from an igneous rock, and paragneiss is one from a sedimentary rock. Gneissose rocks have properties similar to gneiss. 
Formation
Gneiss is formed from sedimentary or igneous rock exposed to temperatures greater than 320 °C and relatively high pressure.
Types
Augen gneiss
Augen gneiss, from the German: Augen [ˈaʊɡən], meaning "eyes", is a coarse-grained gneiss resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shear-bound feldspar porphyroclasts, normally microcline, within the layering of the quartz, biotite and magnetite bands.
Henderson gneiss
Henderson gneiss is found in North Carolina and South Carolina, US, east of the Brevard Shear Zone. It has deformed into two sequential forms. The second, more warped, form is associated with the Brevard Fault, and the first deformation results from displacement to the southwest.
Lewisian gneiss
Most of the Outer Hebrides of Scotland have a bedrock formed from Lewisian gneiss. In addition to the Outer Hebrides, they form basement deposits on the Scottish mainland west of the Moine Thrust and on the islands of Coll and Tiree. These rocks are largely igneous in origin, mixed with metamorphosed marble, quartzite and mica schist with later intrusions of basaltic dikes and granite magma.
Archean and Proterozoic gneiss
Gneisses of Archean and Proterozoic age occur in the Baltic Shield.
AI rock expert in your pocket
Scan QR code to download
