Foliated Metamorphic Rocks: (Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.) Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned.

There are two main types of metamorphic rocks: those that are foliated because they have formed in an environment with either directed pressure or shear stress, and those that are not foliated because they have formed in an environment without directed pressure or relatively near the surface with very little pressure …

differential stress

Foliation in geology refers to repetitive layering in metamorphic rocks. Each layer can be as thin as a sheet of paper, or over a meter in thickness. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and gneiss.

Foliation is caused by the re-alignment of minerals when they are subjected to high pressure and temperature. Individual minerals align themselves perpendicular to the stress field such that their long axes are in the direction of these planes (which may look like the cleavage planes of minerals).

Foliation is the result of the parallel arrangement of (micas, etc.) in a plane perpendicular to the maximum principal applied stress. A lineation is caused by a similar growth of elongate minerals (eg. Slate, schist, and gneiss are three common foliated metamorphic rocks.

Gneiss

Geologists use index minerals that form at certain temperatures and pressures to identify metamorphic grade. These index minerals also provide important clues to a rock’s sedimentary protolith and the metamorphic conditions that created it.

What two features characterize most metamorphic rocks? or alternating light and dark mineral bands) are characteristic of most metamorphic rocks. What phenomena can cause metamorphism? convection, deep burial, and water-rock interactions all lead to metamorphism.

Metamorphic Definition They were once igneous or sedimentary rocks;, however, they have been changed (metamorphosed) when subjected to intense heat and pressure within the Earth’s crust. They are crystalline by nature and often have a “squashed” (foliated or banded) texture.

Factors that Control Metamorphism

• Chemical Composition of the Protolith. The type of rock undergoes metamorphism is a major factor in determing what type of metamorphic rock it becomes.
• Temperature.
• Pressure.
• Fluids.
• Time.
• Regional Metamorphism.
• Contact Metamorphism.
• Hydrothermal Metamorphism.

The main feature that identifies metamorphic rocks is that they are shaped by great heat and pressure. Because their mineral grains grew together tightly during metamorphism, they’re generally strong rocks. They’re made of different minerals than other kinds of rocks and have a wide range of color and luster.

Metamorphic rocks have been on Earth for millions of years. They can be different shapes, sizes, and colors. Metamorphic rocks are used to make buildings, jewelry, powders, and other things. They are an important part of our world.

Quartzite and marble are the most commonly used metamorphic rocks. They are frequently chosen for building materials and artwork. Marble is used for statues and decorative items like vases (Figure). Schist and slate are sometimes used as building and landscape materials.

Marble, quartzite, and soapstone are examples of non-foliated metamorphic rocks. Marble (left) and quartzite (right) are non-foliated metamorphic rocks.