18 Questions
What is the main characteristic of gneisses?
Gneisses are characterized by gneissic layering.
Which type of minerals are responsible for the alternating light-colored bands in gneisses?
Quartz and feldspar
What can rigid feldspar grains sheared into oval eye-shaped crystals produce in gneisses?
Augen gneiss
What is the term for lens-shaped grains that quartz grains in gneisses can be sheared into?
Flaser
What are orthogneisses and paragneisses determined by?
Their protoliths
Which type of protolith can result in gneisses referred to as granite gneiss?
Granites
What is the main reason behind the development of gneissic foliations?
Layer transposition and segregation of minerals
In gneissic banding, which type of minerals are typically concentrated in fold limbs?
Micas and inosilicate minerals
What process results in the production of igneous layers enriched in quartz and feldspar between refractory layers enriched in dark-colored ferromagnesian minerals?
Partial melting (anatexis) and differentiation
Which type of minerals have higher melting temperatures compared to quartzofeldspathic minerals according to the text?
Dark-colored ferromagnesian minerals
What role does layer transposition play in the development of gneissic banding?
It pulls apart earlier folded layers leading to separate light and dark bands
Which process is responsible for the development of gneissic foliations by creating alternating light and dark color bands?
Layer transposition
What does a 'lit par lit intrusion' refer to?
Intrusion of granitic magma into mafic country rock
What characteristic makes gneisses unsuitable for easy splitting?
Crude foliation
At what temperature range do gneisses typically form in dynamothermal settings?
600°C and above
Which type of rocks possess both igneous and metamorphic characteristics?
Migmatites
What is a distinguishing feature of migmatites compared to gneisses?
Irregular, swirling mix of colors
At what temperature can extensive melting of gneiss lead to the formation of migmatites?
~700°C
Learn about gneiss, a metamorphic rock characterized by gneissic layering with distinct color bands. Explore the minerals found in gneisses including quartz, feldspar, biotite, amphibole, pyroxenes, garnet, sillimanite, cordierite, and corundum.
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