What two features can develop in a rock during metamorphism?
The correct answer and explanation is :
Two key features that can develop in a rock during metamorphism are foliation and non-foliated texture.
1. Foliation:
Foliation refers to the alignment of mineral grains in a rock, often appearing as layers or bands. It develops in response to directed pressure or differential stress during metamorphism. When rocks are subjected to intense pressure, minerals like mica, chlorite, and feldspar tend to align parallel to the stress direction. This alignment creates a layered or banded structure in the rock. Foliation is most commonly seen in metamorphic rocks such as schist, slate, and gneiss.
Foliation can form in several stages, depending on the type of metamorphism. In slate, the minerals are aligned in very fine layers, while in schist and gneiss, the minerals are coarser and the layers are more pronounced. The degree of foliation depends on the amount of pressure, temperature, and the type of parent rock.
2. Non-foliated Texture:
In contrast to foliation, non-foliated metamorphic rocks do not develop any layer-like structures. Instead, the minerals in these rocks are typically interlocked in a granular texture. Non-foliated textures form under conditions of uniform pressure or when the rock is primarily made up of one mineral that does not align under pressure.
Non-foliated rocks include marble, which forms from limestone, and quartzite, which forms from sandstone. Marble has a smooth, crystalline texture and results from the recrystallization of calcite under heat and pressure. Quartzite is similarly a crystalline rock but is formed from quartz-rich sandstone under intense heat and pressure.
Conclusion:
The development of foliation or non-foliated textures during metamorphism is influenced by factors such as the type of parent rock, the degree of heat and pressure, and the presence of fluids. Foliation results from directed pressure causing minerals to align, while non-foliated textures form in environments where uniform pressure or lack of mineral alignment prevails.