What are the factors that affect metamorphism?
The main factors that control metamorphic processes are:
- The mineral composition of the parent rock.
- The temperature at which metamorphism takes place.
- The amount and type (direction) of pressure during metamorphism.
- The amount and type of fluid (mostly water) that is present during metamorphism.
What’s the difference between regional and contact metamorphism?
Contact metamorphism is a type of metamorphism where rock minerals and texture are changed, mainly by heat, due to contact with magma. Regional metamorphism is a type of metamorphism where rock minerals and texture are changed by heat and pressure over a wide area or region.
How is the orientation of foliation related to stress?
Most foliation is caused by the preferred orientation of phylosilicates, like clay minerals, micas, and chlorite. Preferred orientation develops as a result of non-hydrostatic or differential stress acting on the rock (also called deviatoric stress).
Why is phyllite shiny?
Phyllite is a fined grained metamorphic rock. It is foliated, meaning that it has noticeable layers, and splits easily. A defining characteristic is the shiny surface, called phylitic luster caused by the mica particles within the rock. It is associated with regional metamorphism due to mountain building.
What level of metamorphism is phyllite formed?
Phyllite is formed by relatively low-grade metamorphic conditions in the lower part of the greenschist facies. Parent rocks may be only partially reconstituted so that the original mineralogy and sedimentary bedding are partially preserved.
What does phyllite turn into?
Phyllite is associated with regional metamorphism due to mountain building. Continued metamorphism converts clay minerals into large grains of mica, along with quartz and feldspar. At that point, phyllite becomes schist.
What Colour is phyllite?
Phyllite is a foliated metamorphic rock rich in tiny sheets of sericite mica. It presents gradation in degree of metamorphism ranging between slate and mica schist. The color varies between black and gray to greenish-gray (Fig.
Does phyllite have crystals?
Phyllite is composed mainly of tiny grains of mica minerals such as muscovite, or sericite. Crystals of other metamorphic minerals such as andalusite, biotite, cordierite, garnet, and staurolite might also form within phyllite. Their crystals often grow large enough to be seen and identified with the unaided eye.
What does phyllite mean?
: a foliated rock that is intermediate in composition and fabric between slate and schist.
How does phyllite turn into schist?
To become schist, a shale must be metamorphosed in steps through slate and then through phyllite. If the schist is metamorphosed further, it might become a granular rock known as gneiss.
What is difference between slate and phyllite?
Slate is a low grade metamorphic rock that is generally formed by metamorphosis of mudstone or shale, under relatively low pressure and temperature conditions. Phyllite is a metamorphic rock which is formed by regional metamorphism of argillaceous sediments since their cleavage arose due to deviatoric stress.
Is phyllite contact or regional?
| Summary Chart of Common Metamorphic Rocks | ||
|---|---|---|
| Original Rocks | Metamorphic Equivalent | Metamorphism |
| sandstone | quartzite | regional & contact |
| shale | slate >> phyllite >> schist >> gneiss | regional |
| limestone | marble | contact |