What is Porphyroclastic texture?
Porphyroclasts are single crystals of a size exceeding the mean grain size in the surrounding matrix and typical for mylonites. They are relic structures of a more coarse-grained original fabric. Common minerals that form porphyroclasts are feldspar, garnet, muscovite, hornblende and pyroxenes.
Which one is a metamorphic texture?
Foliation is common in aphanitic as well as phaneritic metamorphic rocks. Some foliated rocks are also banded….
| Metamorphic Rocks | BANDED |
|---|---|
| PHANERITIC | |
| Medium- to coarse-grained, GNEISSOSE texture | |
| ROCK NAME | GNEISS |
| PROTOLITH (Original Rock) | Sandstone Granite or other Igneous Rock |
What is the difference between Porphyroclast and porphyroblast?
A porphyroblast is a large mineral crystal in a metamorphic rock which has grown within the finer grained matrix. Porphyroblasts are often confused with porphyroclasts, which can also be large outstanding crystals, but which are older than the matrix of the rock.
What does Schistosity mean in geology?
schistosity, mode of foliation that occurs in certain metamorphic rocks as a consequence of the parallel alignment of platy and lath-shaped mineral constituents. It reflects a considerable intensity of metamorphism—i.e., changes resulting from high temperatures, pressures, and deformation.
What is Granoblastic texture?
Granoblastic is an adjective describing an anhedral phaneritic equi-granular metamorphic rock texture. Granoblastic texture is typical of quartzite, marble, charnockites and other non-foliated metamorphic rocks without porphyroblasts. A rock that has a granoblastic texture can be termed a granofels.
What is Cataclastic texture?
1 : of, relating to, or caused by cataclasis a pronounced cataclastic texture. 2 : having the granular fragmental texture induced in rocks by mechanical crushing cataclastic structures.
What is palimpsest texture?
Said of a structure or texture of metamorphic rocks in which remnants of some pre-existing structure or texture are preserved.
What is Lepidoblastic texture?
A lepidoblastic texture is a metamorphic texture in which platy or tabular minerals are aligned to produce a planar fabric. This texture is due to the parallel orientation during recrystallization of minerals with a flaky or scaly habit, e.g. mica and chlorite.
What is gneissic texture?
The “gneissic texture” refers to the segregation of light and dark minerals. It is indicative of high-grade metamorphism where the temperature is high enough, say 600-700 °C, so that enough ion migration occurs to segregate the minerals. Gneiss often forms from the metamorphism of granite or diorite.
How do you identify Schistosity?
Schistosity differs from slaty cleavage in both grain size and mineral content. The layering in a rock in which bands or lenses of granular minerals (quartz and feldspar) alternate with bands or lenses in which platy (mica) or elongate (amphibole) minerals predominate.
Where does metasomatism occur?
Metasomatism takes place in some rocks adjacent to igneous intrusions (see Contact (thermal) metamorphism; Skarn). It may also affect extensive areas (regional metasomatism), with the introduction of fluids possibly related to partial fusion at depth.