Metamorphic Rocks

Experiment: (here are two)

Squeeze your hand together really hard for a while. You will begin to feel some warmth and some pressure. This is essentialy what is happening to rocks to cause them to become metamorphic.

How are metamorphic rocks formed-
Metamorphic rocks are formed by processes of extreme heat and pressure. All metamorphic rocks were once igneous or sedimentary rocks, but after time of the rocks being exposed to ton and tons of heat and pressure they change and form into a new type of rock. The basic science behind this process is that the extreme heat and prssure breaks apart some of the atoms in the rocks. If all of them atoms were to break apart the rock would melt, and it would be an igneous rock. By not melting their atoms form new bonds and make the more stable for the enviorment the rock is in.

external image 6gneiss-folds58.jpg
Here is a metamorphic rock that you
can easily see how the sturucture has
changed from heat and pressure

Foliated vs Non-foliated

Foliated Metamorphic Rocks- A foliated rock is a metamorphic rock that has visual bands (lines) running on its sides. The process by which this is done is that the imense heat and pressure cause the metamorphic rock to lengthen and flatten. However the pressure is not great enough to creat new mineralization. The bands are allined perpendicular to the greatest pressure.


Non-foliated Metamorphic Rocks- A non-foliated rock is a metamorhic rock where sediments are underground enough to where heat and pressure begin to affect them. Unlike foliated rocks where the pressure generally comes from one side to cause them to band non-foliated rock have pressure applied to them from all areas more evenly. This in turn doesn't result of a banding of the mineral.


Types of metamorphism: (

Contact metamorphism:
Contact metamorphism is basicly know as high heat low pressure metamorphism. What essientally this means is that
change take place when magma is injected into the surrounding solid rock causing it to change its structure. This is usually as more localized area.
Metamorphism is restricted to the zone surrounding the intrusion. Rocks outside of the contact zone aren't affected by the intrusive event. The grade of metamorphism increases in all directions toward the intrusion. Due to the temperature contrast between the surrounding rock and the intruded magma contact metamorphism is often referred to as high temperature, low pressure metamorphism. The rock produced is often a fine-grained rock that shows no foliation, called a hornfels.
Regional Metamorphism:
Regional metamorphism occurs over large areas and generally does not show any relationship to igneous bodies. Most regional metamorphism is accompanied by deformation under non-hydrostatic or differential stress conditions. Regional metamorphism usually results in forming metamorphic rocks that are strongly foliated, such as slates, schists, and gniesses. The differential stress usually results from tectonic forces that produce compressional stresses in the rocks, such as when two continental masses collide. Thus, regionally metamorphosed rocks occur in the cores of fold/thrust mountain belts or in eroded mountain ranges. Compressive stresses result in folding of rock and thickening of the crust, which tends to push rocks to deeper levels where they are subjected to higher temperatures and pressures.

Types of Metamorphic Rocks:


Metamorphic Rock Uses:

Uses of common metamorphic rocks.

SCHIST: A metamorphic uneven-granular, medium to coarse grained, crystalline with prominent parallel mineral orientation. Goes from silvery white to all shades of gray with yellow to brown tones depending on the mineral concentration. Some schists have graphite and some are used as building stones.

GNEISS: A metamorphic uneven granular medium to coarse grained crystalline with more or less parallel mineral orientation. Colors are too variable to be of diagnostic value. Due to physical and chemical similarity between many gneisses and plutonic igneous rocks some are used as building stones and other structural purposes.

QUARTZITE: A metamorphic or sedimentary rock with crystalline texture, consists of rounded quartz grains cemented by crystalline quartz, generally white, light gray or yellow to brown. Same uses as sandstone.


MARBLE: A metamorphic even-granular grain to medium grained and may be uneven granular and coarse grained in calc-silicate rock. The normal color is white but accessory minerals act as coloring agents and may produce a variety of colors. Depending upon its purity, texture, color and marbled pattern it is quarried for use as dimension stone for statuary, architectural and ornamental purposes. Dolomite rich marble may be a source for magnesium and is used as an ingredient in the manufacture of refracting materials.