Chapter 7- Metamorphic Minerals and Rocks

Physical Geology Illustrated Vocabulary     
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Roger Weller, geology instructor
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serpentine   

metamorphic rocks videos
 metamorphic rocks  (30)

Chapter 7- Metamorphic Materials
copyright 2016-Roger Weller
last edited: 3/23/16

chill zone
-is the outer part of a magma body that cools quicker because
it is in contact with the cooler country rock;  
consequently grain sizes in this region are smaller than for the
rest of the magma body.

-chill zone-Opal's  Pals

compression
-is a squeezing force that tends to flatten an object.

contact metamorphism
-is a form of metamorphism where rocks are baked by the heat from an igneous intrusion.
-contact metamorphism-Opal's Pals

country rock
-is the pre-existing rock that into which a magmatic intrusion invades.
-country rock-Opal's Pals

epidote
-is a pistachio or pea soup green silicate mineral; often found in a massive state as a coating on
fault surfaces.

-Mt. Whitney-fault surface with epidote-A 
-Mt. Whitney-fault surface with epidote-B 
-epidote as slickensides-Huachuca Mountains 
-epidote-Opal's Pals


fissility
-is the property of a rock, such as shale or slate, of splitting into thin layers
-flat fragments of slate 

folds
-occur when layered or foliated materials, such as gneiss or schist, are subjected to compressional
forces perpendicular to the layering.

-gneiss folds:  1  2  3
-folds-Opal's  Pals


foliation
-is the layering of flat minerals, usually mica, in metamorphic rocks such as schist and gneiss.
-mica schist 
-gneiss-cut 


garnet
-is a silicate mineral family that forms somewhat rounded crystals in the isometric system.
Common shapes are dodecahedrons (12 sided) and trapezohedrons (24 sided). Depending upon its
quality this mineral can be used either for abrasives (sandpaper) or gemstones (usually red).

-garnet in schist-A 
-garnet in schist-B 
-garnet-dodecahedrons 
-garnet-trapezohedron 
-garnet-Opal's  Pals


gneiss
-is a rock metamorphosed at high temperatures.  It is often layered with dark and light minerals,
or it may have its dark minerals all pointing in the same direction (lineation). 
Commonly, gneisses may show complex folding.

-banded gneiss
-lineated gneiss
-folded gneiss
-gneiss-Opal's Pals


hornfels
-is a non-foliated metamorphic rock commonly produced by the baking of shale or basalt by the
heat from a nearby igneous intrusion.

-hornfels-A 
-hornfels-B 

jade
-is also known as nephrite jade; a variety of amphibole.
-jade-pebble 
-large jade boulder 
-polished jade slab 


jadeite
-is sometimes called jadeite jade; a variety of pyroxene.
-jadeite, bracelets 
-jadeite, carving 

kyanite
-is a metamorphic mineral that forms flat, blade-like blue crystals.

-kyanite-A 
-kyanite-B 
-kyanite-C 
-kyanite-D 


lineation
-refers to elongated minerals within a metamorphic rock are aligned in the same direction; often
seen in gneisses.

-gneiss, lineation-1 
-gneiss, lineation-2 


marble
-is a metamorphic rock formed from limestone or dolomite that has been recrystallized.
The most commonly identified form of this material is white with gray streaks, but over 300
varieties of different colors and patterns have been recognized.

-marble, polished breccia-A 
-marble, polished breccia-B 
-marble, polished-swirl pattern-A 
-marble, polished-swirl pattern-B 
-marble-Opal's Pals


metaconglomerate
-is a metamorphosed conglomerate. Often identified by the presence of elongated and parallel
aligned pebbles.


metamorphic minerals
-minerals that commonly occur because of metamorphism are:

-amphibole
-chrysotile asbestos
-epidote
-garnet
-graphite
-jadeite
-kyanite
-mica
-nephrite jade
-serpentine
-sillimanite
-staurolite
-talc
-wollastonite

metamorphic rock
-is a rock that has been altered from its original condition by heat and/or pressure.

-slate 
-mica schist 
-gneiss 
-marble 

metamorphism
-is the process of altering the chemistry and/or structure of a rock through heat and/or pressure.


mica schist
-is a foliated metamorphic rock between phyllite and gneiss that is made up of sparkly, small mica
crystals.

-mica schist-A 
-mica schist-B 

phyllite
-is a foliated metamorphic rock between slate and schist; often has a silky appearance and a
slightly wavy surface.

-phyllite-A 
-phyllite-B 

ptygmatic folds
-are intricately folded veins found in granitic and metamorphic rocks.

-ptygmatic folds-A 
-ptygmatic folds in xenolith surrounded by granite 

quartzite
-is the metamorphic rock that started out as a sandstone; consists of well cemented quartz sand
grains.

-quartzite

regional metamorphism
-occurs when a large region has been metamorphosed due to a major tectonic event such as
collision of continents.
-regional metamorphism-Opal's Pals

schist
-is a foliated metamorphic rock, more metamorphosed than phyllite, but less metamorphosed than
gneiss; often has a sparkly surface due to the reflection of light from a myriad of tiny mica crystals.

-mica schist-A 
-mica schist-B 
-schist-Opal's Pals

serpentine
-is a non-foliated sedimentary rock ranging in color from yellow green to dark green to nearly
black; closely resembles jade but is far less durable.

-serpentine 

shear
-is the type of stress where one block slides past another block; materials caught between the two
blocks are said to be undergoing shear.

sillimanite
-is a white metamorphic mineral.
-sillimanite
-sillimanite-Opal's  Pals

skarn
-Limestones or dolomites that have been silicified and mineralized with iron, magnesium, and
aluminum silicates as part of a metamorphic process.
-skarn

slate
-is a metamorphic rock, often gray or black in color, that splits into very flat sheets; produced by
the metamorphism of shale.

-slate 

staurolite
-is a brown-colored metamorphic silicate mineral that often forms interpenetration twins in the
form of crosses where the crystals can occur at 90 degrees or 60 degrees.

-staurolite, crystals 
-right-angle staurolite twin crystal from Russia
-staurolite crystals in schist 

talc
-is a metamorphic mineral, typically white or pink, that is extremely soft. When ground to a fine
powder with some added perfume, it becomes talcum powder.

-talc, white 
-talc-Opal's Pals


wollastonite
-is a white metamorphic mineral with the chemical composition of calcium silicate.
It is the mineral
that forms as cement hardens, formed from calcium oxide plus silica.

-wollastonite

xenolith
-is a baked inclusion of country rock surrounded by an intrusive igneous rock.

-xenoliths-A 
-xenolith-B 
-xenoliths-Opal's Pals


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