and Processes that create them Metamorphic Rocks and Processes that create them

Metamorphic Rocks Less common than sedimentary or igneous rocks. Created by a process called METAMORPHISM  Meta (change) morph (form). 

METAMORPHISM Process by which extreme heat, pressure or chemicals, changes the mineralogy, texture, and chemical composition of existing rocks. As we descend into the earth the temperature increases about 25 degrees Celsius for every kilometer that we descend.

METAMORPHISM PRESSURE squeezes grains in the rocks, making them more dense and less porous.  HEAT and CHEMICALS can also rearrange the particles.  NEW minerals may be formed. Eg. Quartzite is metamorphosed sandstone, both made of Quartz Eg. Marble is metamorphosed limestone, both made of calcite.

TWO TYPES OF METAMORPHISM: Regional Metamorphism Contact Metamorphism https://youtu.be/Bbw8BiZhGg0

REGIONAL METAMORPHISM: When heat, pressure and directed stress are simultaneously applied to pre existing rock. Occurs over large areas Eg. Mountain-building movements Heat comes from friction of moving rock layers and heat from deep within Earth's crust Pressure comes from both weight of overlying rocks and squeezing of the moving rock masses. 

CONTACT METAMORPHISM: Occurs when hot magma or lava heat pre-existing rock, changing the crystallization Occurs over smaller areas. Changes to rock are less drastic

Contact Metamorphism Magma has pushed its way into layers of limestone, sandstone and shale. The heat generated by the magma has changed these sedimentary rocks to metamorphic rocks marble, quartzite, and hornfels.

HOW ARE METAMORPHIC ROCKS CLASSIFIED? All rocks are classified by TEXTURE (grain size, shape, orientation) and mineral COMPOSITION. But....

HOW ARE METAMORPHIC ROCKS CLASSIFIED? There are many combinations of heat, pressure, and chemically active fluids and therefore many different products.  And any kind of rock can be a parent rock (sedimentary, igneous, other metamorphic rocks)

HOW ARE METAMORPHIC ROCKS CLASSIFIED? So the same heat/pressure/fluid combination can produce different results depending on the parent rock, And different parent rocks may undergo any kind of metamorphism and end up looking virtually the same. 

HOW ARE METAMORPHIC ROCKS CLASSIFIED? So … there is no direct relationship between the processes of metamorphism and the rocks that result. So…how do we classify metamorphic rocks?      

Metamorphic Rocks are Broadly Classified in two groups: FOLIATED            or   NON-FOLIATED

Foliation Foliated means leaf in Latin. Most metamorphic rocks are foliated.

Foliated Metamorphic Rocks Foliation is a banding pattern due to intense but unequal pressures in more than one direction.

Foliated Metamorphic Rocks Form when pressure causes long flat minerals in the original rock to align.

How is foliation different than sedimentary layering? Foliation is the squeezing of long minerals within a rock into a banding pattern. Sedimentary layers are due to many different deposits occurring at different times.

Foliation is determined by type of Metamorphism Foliated rocks usually produced by Regional Metamorphism Non-foliated rocks usually produced by Contact Metamorphism due to lack of pressure

Foliation ranges from very fine (microscopic) to very coarse.

Increasing intensity of metamorphism produces more coarse (visible) foliation.

Examples of Foliated Rocks When SHALE undergoes metamorphism, the rock becomes more dense and more crystalline. The elements recombine to form new minerals not found in shale such as mica and hornblende.  Pressures squeeze the flakes of mica or the needles of hornblende into PARALLEL LAYERS Foliate comes from the Latin word that means sheets, as in the sheets of paper in a book.

Examples: Slate First to form from metamorphism of shale. Very fine grains Very low grade metamorphism Breaks into sheets has microscopically thin foliation layers.  

Blackboards Are made of slate

Slate Roofs Slate consists of minerals that are stable and resistant to weathering and has high strength, low porosity, and low absorption. The low porosity and low absorption of slate make it well adapted for roofing purposes. The two most important structural properties of slate are cleavage and grain.

Phyllite Further metamorphism may create shiny PHYLLITE. Fine grains Low grade metamorphism

SCHIST Further metamorphism may create flaky SCHIST. Coarse grains Found in sites of “medium grade” metamorphism Has foliation layers that are easily seen with naked eye. As schist can come from many different rocks, it is usually named for its principal material: mica schist, talc schist, hornblende schist, etc.

Schist

Schist Waiho Valley, New Zealand. Schist eroded by a glacier.

GNEISS Can form from shale, granite, conglomerate etc. Very coarse grains Coarsest foliation ‘high-grade’ metamorphism Alternating light and dark bands

Gneiss Gneiss had streaked banded of alternating light and dark minerals.

Metamorphic Mountains Mixup Mountain, gneiss Eldorado Peak, gniess Cascade Peak, schist

Non-Foliated Rocks No banding pattern Less common Created mostly by Contact Metamorphism Eg. Marble, quartzite, hornfels

Homework Answer #19-23 on page p79 of text.

Michelangelo's Pieta Marble. Results from the metamorphism by heat of limestone or dolomite. Usually whitish, but marble can be found in other colours due to impurities. Marble used by Italian sculptors is always free of impurities.

Marble Quarry Carrara, Italy in the Appenines Mountains in Tuscany. Renowned for its purity and lack of fractures.

Jade Jade is a metamorphic rock, which forms under medium to high-grade metamorphism during regional metamorphism of mafic and ultramafic rocks. Minerals nephrite or jadeite. Can be coloured white, grey, or various shades of green.

Where to Find Jade in B.C.?

Geologists have their schist together. Don’t take the schist for granite

Rock Cycle https://www.forbes.com/sites/trevornace/2016/02/21/rock-cycle-kids-types-rocks-minerals/#5d8e248640b5