Metamorphic Petrology- Types of Metamorphism, Protoliths, Textures, & Classification | GEO GIRL

Summary

This video delves into metamorphic petrology, explaining the process of metamorphism as recrystallization under high temperature and pressure. It distinguishes between types of metamorphism, such as regional and contact, and discusses how to determine a rock's protolith. The video also explores the classification of metamorphic rocks based on both structural characteristics, like foliation and schistosity, and compositional aspects, including examples like marble and quartzite. It aims to provide a foundational understanding of the subject for viewers.

Takeaways

• 🔥 Metamorphism in geology refers to the recrystallization of a rock under high temperature and pressure conditions.
• 🌡️ Different types of metamorphism, such as regional and contact metamorphism, involve varying degrees of heat and pressure.
• 🏔️ Regional metamorphism occurs on a large scale, often due to subduction zones or plate boundaries, while contact metamorphism is caused by the heat from magma intrusions.
• 🌋 The line between metamorphism and other processes like diagenesis and igneous activity can be blurry, especially at low and high temperatures, respectively.
• 💠 The goals of metamorphic petrology include determining the protolith of a rock, the conditions of metamorphism, and the structural history of the rock.
• 🗝️ Determining the protolith of a metamorphic rock can be straightforward in cases like marble (limestone) and quartzite (sandstone), but it can be complex for rocks like basalt.
• 📏 Metamorphic textures can be primary, preserved from the original rock, or secondary, formed during metamorphism, and include static and tectonic textures.
• 📚 The script introduces various types of metamorphic rocks, such as gneiss, schist, and slate, each with distinct characteristics and textures.
• 📖 Metamorphic rocks can be classified based on their structure, like granofels and hornfels, or composition, like green schist and eclogite.
• 🔍 The script emphasizes the importance of understanding metamorphic textures and rock types for interpreting the geological history and environment of rock formation.

Q & A

What is metamorphism in geology?

Metamorphism in geology is the recrystallization of a rock under high temperature and pressure, where different types of metamorphism have varying amounts of pressure and temperature acting on the rock.

How does contact metamorphism differ from regional metamorphism?

Contact metamorphism is dominated by heat from intrusions like magma chambers or plutons coming into contact with country rock, causing metamorphism primarily due to heat rather than pressure. In contrast, regional metamorphism occurs on a larger scale, often due to subduction zones or plate boundaries, and involves both high temperatures and pressures.

What is the difference between metamorphism and diogenesis?

The line between metamorphism and diogenesis can be distinguished based on the participation of clastic grains in reactions with pore water and the precipitates from that water. Diogenesis involves the cementation of clastic grains in a sedimentary environment, while metamorphism occurs at higher temperatures and pressures where these grains react with the cement or pore water.

What are the three major goals of studying metamorphic petrology?

The three major goals of studying metamorphic petrology are to determine the protolith of the metamorphic rock, the conditions of the metamorphism such as temperature, pressure, and fluid composition, and the structural history of the rock including whether it was deformed before, during, or after metamorphism.

Why are metamorphic rocks harder than their sedimentary protoliths?

Metamorphic rocks are harder than their sedimentary protoliths because they become densely packed and recrystallized under pressure, which causes the grains to be much harder.

How can you determine the protolith of a metamorphic rock?

The protolith of a metamorphic rock can often be determined by its composition. For example, marble is the metamorphic rock that forms from limestone, quartzite typically has a sandstone protolith, and gneiss is often the metamorphic version of granite.

What are primary textures in metamorphic rocks?

Primary textures in metamorphic rocks are those that form during deposition of sedimentary rocks or during crystallization of igneous rocks. These can sometimes be preserved in metamorphic rocks if the metamorphism was relatively low grade or the original rock was sturdy enough to preserve some of its primary texture.

What are static and tectonic textures in metamorphic rocks?

Static textures in metamorphic rocks refer to minerals that grew or recrystallized without deformation or after deformation, resulting in equant or equal-sized grains. Tectonic textures, on the other hand, develop during or before deformation, showing foliation, schistosity, and lineation due to the preferred orientation of minerals.

How are metamorphic rocks classified structurally and compositionally?

Metamorphic rocks can be classified structurally using terms like granofels, hornfels, slate, phyllite, schist, and gneiss, which describe the rock's texture and structure. Compositionally, they can be classified based on their mineral assemblages, such as green schist, amphibolite, granulite, eclogite, marble, quartzite, and serpentine.

Why is it sometimes difficult to determine the protolith of a basalt-derived metamorphic rock?

It is sometimes difficult to determine the protolith of a basalt-derived metamorphic rock because basalt can have many different compositions, structural varieties, and a lot of variety that makes its final metamorphic equivalent hard to determine. The metamorphic grade also plays a role, as high-grade metamorphism results in different rock types than low-grade metamorphism.

Outlines

00:00

🌋 Introduction to Metamorphic Petrology

The paragraph introduces metamorphic petrology, focusing on metamorphic metrology and its various aspects. It discusses different types of metamorphism, such as regional and contact metamorphism, and touches on the distinction between metamorphism and diagenesis. The explanation includes the effects of temperature and pressure on rocks and how these factors lead to recrystallization. The paragraph also differentiates between metamorphism and igneous processes, highlighting the importance of understanding the conditions under which metamorphic rocks form.

05:05

🔍 Goals of Metamorphic Petrology

This section outlines the three main objectives of studying metamorphic petrology: determining the protolith of metamorphic rocks, understanding the conditions of metamorphism, and examining the structural history. It explains the significance of identifying the original rock type before metamorphism and the environmental implications. The paragraph also delves into the importance of recognizing the temperature, pressure, and fluid composition during metamorphism and how these elements influence rock transformation.

10:06

🪨 Determining Protoliths of Metamorphic Rocks

The paragraph discusses methods for determining the protolith of metamorphic rocks, using examples such as marble and limestone, quartzite and sandstone, and schist and shale. It also addresses the challenges in identifying the protolith of certain rocks like basalt due to their compositional variety. The discussion includes the concept of metamorphic grade and how it affects the appearance and classification of metamorphic rocks, as well as the distinction between low-grade and high-grade metamorphism.

15:12

🌈 Metamorphic Textures and Their Significance

This section explores the importance of textures in understanding metamorphic rocks, distinguishing between primary textures preserved from the original rock and secondary textures formed during metamorphism. It explains static and tectonic textures, providing examples of each and how they reveal information about the rock's history and metamorphic environment. The paragraph also covers the preservation of sedimentary and igneous textures in metamorphic rocks and how these can be identified.

20:14

📚 Classification of Metamorphic Rocks

The paragraph discusses the classification of metamorphic rocks based on both structural and compositional terms. It defines various structural classifications such as granofels, hornfels, slate, phyllite, schist, gneiss, and others, explaining the characteristics that distinguish them. The compositional classification is also introduced, mentioning examples like green schist, amphibolite, and eclogite, and how they are identified by their mineral assemblages. The summary emphasizes the importance of recognizing these classifications for understanding the rock's metamorphic history.

25:17

📖 Conclusion and Resources for Metamorphic Petrology

In the concluding paragraph, the speaker summarizes the key points covered in the video and provides resources for further learning. They mention the book 'Essentials of Igneous and Metamorphic Petrology' by Ronald and Carol Frost as a reference and encourage viewers to explore more videos on the topic in the upcoming playlist. The paragraph serves as a wrap-up, thanking viewers for their time and setting expectations for future content.

Keywords

💡Metamorphism

Metamorphism refers to the process of transformation of existing rock types, but in a solid state, through subjection to different temperature and pressure conditions within the Earth's crust. In the video, metamorphism is a central theme, with the speaker elaborating on how rocks undergo recrystallization due to high temperatures and pressures, leading to the formation of metamorphic rocks. Examples given include contact metamorphism, which is dominated by heat, and regional metamorphism, which involves both heat and pressure.

💡Metamorphic petrology

Metamorphic petrology is a sub-discipline of geology that studies the origin, evolution, and classification of metamorphic rocks. The video introduces metamorphic petrology as a field that encompasses understanding the different types of metamorphism and the characteristics of the resulting rocks. It is integral to the video's narrative as it sets the stage for discussing various aspects of metamorphic rocks and their formation.

💡Protolith

The protolith is the original rock that existed before it was subjected to metamorphism. In the context of the video, determining the protolith of a metamorphic rock is one of the primary goals of metamorphic petrology. The speaker uses examples such as marble, which has limestone as its protolith, and quartzite, which typically has a sandstone protolith, to illustrate how the composition of metamorphic rocks can provide clues about their original forms.

💡Metamorphic grade

Metamorphic grade refers to the intensity of metamorphism a rock has undergone, which is typically classified as low, medium, or high grade. The video discusses how different grades of metamorphism can result in different types of metamorphic rocks. For instance, shale under low-grade metamorphism becomes slate, while under high-grade conditions, it becomes schist.

💡Texture

In geology, texture refers to the arrangement of grains or crystals in a rock. The video emphasizes the importance of studying textures in metamorphic rocks to understand their structural history and the metamorphic environment they formed in. The speaker differentiates between primary textures, which may be preserved from the original rock, and secondary textures, which are formed during metamorphism.

💡Contact metamorphism

Contact metamorphism is a type of metamorphism that occurs when rocks are heated by the intrusion of magma or plutons, leading to changes in the rock's mineralogy and texture. The video script describes how contact metamorphism is dominated by heat rather than pressure, resulting in distinct textures compared to regional metamorphism. An example from the script is the metamorphism of country rock near an intrusive body.

💡Regional metamorphism

Regional metamorphism affects large areas of rock and is typically associated with tectonic events such as subduction or collision of continental plates. The video explains that regional metamorphism involves both high temperatures and pressures, leading to significant changes in rock composition and texture. This is contrasted with contact metamorphism, which is primarily a thermal event.

💡Hydrothermal metamorphism

Hydrothermal metamorphism is a process where hot water circulates through rocks, causing chemical reactions and leading to metamorphism. The video mentions this type of metamorphism in the context of oceanic crust, where hydrothermal fluids react with newly formed igneous minerals, transforming them into micas and clays.

💡Schist

Schist is a type of metamorphic rock characterized by a banding or foliation caused by the alignment of platy minerals like micas. The video discusses schist as a high-grade metamorphic rock derived from shale, where the original clay minerals transform into mica under high temperature and pressure conditions.

💡Gneiss

Gneiss is a banded metamorphic rock that forms from the metamorphism of igneous or sedimentary rocks. The video script uses gneiss as an example of a rock that can be identified by its compositional banding, which is a result of the differential metamorphism of minerals within the rock.

💡Hornfels

Hornfels is a fine-grained, hard metamorphic rock that breaks with a concoidal fracture, similar to glass. In the video, hornfels is mentioned as a product of contact metamorphism where the original rock, often shale or mudstone, undergoes thermal metamorphosis but does not experience significant pressure, resulting in a rock that is much harder than its protolith.

Highlights

Introduction to metamorphic petrology and its various aspects.

Definition of metamorphism as the recrystallization of rock under high temperature and pressure.

Differentiation between metamorphism and diagenesis based on the involvement of clastic grains and pore water reactions.

Explanation of the blurry line between metamorphism and igneous processes at high temperatures.

Types of metamorphism including regional, contact, burial, dynamic, hydrothermal, and impact metamorphism.

The three major goals of studying metamorphic petrology: determining protolith, conditions of metamorphism, and structural history.

Methods to determine the protolith of a metamorphic rock, such as compositional analysis.

The hardness of metamorphic rocks compared to their sedimentary protoliths due to recrystallization under pressure.

Examples of easily identifiable protoliths in metamorphic rocks like marble and quartzite.

Challenges in determining the protolith of basalt due to its compositional variety.

The significance of coal's position on the boundary between diagenesis and metamorphism.

Importance of observing textures in metamorphic rocks to understand their structural history and metamorphic environment.

Classification of metamorphic textures into primary, static, and tectonic textures.

Description of primary textures preserved in metamorphic rocks from sedimentary and igneous origins.

Explanation of static textures in metamorphic rocks, such as equant grains and dihedral angles.

Identification of tectonic textures like foliation, schistosity, and lineation in deformed metamorphic rocks.

Structural classification of metamorphic rocks into terms like granofels, hornfels, slate, phyllite, schist, and gneiss.

Compositional classification of metamorphic rocks based on mineral assemblages, such as green schist, amphibolite, and eclogite.

Practical identification tips for common metamorphic rocks like serpentine, quartzite, marble, and eclogite.

Transcripts

hi everyone today we're talking about metamorphic  petrology and in today's video specifically we'll  

be going over an introduction to metamorphic  metrology and all that it encompasses including  

different types of metamorphism including but  not limited to regional and contact different  

types of metamorphic rocks their metamorphic grade  their proto-list their textures and all of that  

so let's get started first what is metamorphism  metamorphism in geology is the recrystallization  

of a rock under high temperature and pressure and  i say and or pressure here just because different  

types of metamorphism have different amounts  of pressure and temperature that are acting on  

the rock two metamorphosis for example contact  metamorphism is really more heat than it is  

pressure that metamorphoses the rock and  regional metamorphism is more so heat and  

pressure that is causing the metamorphism of that  rock at low temperature however the line between  

metamorphism and diogenesis can become a little  fuzzy but we can at least partially distinguish  

these two processes based on the participation  of clastic grains in reactions with pore water  

in the pore spaces of those clastic grains  as well as the precipitates that might be  

precipitating from that water what does that mean  well clastic or detrital sediment grains that are  

accumulating and becoming buried in a sedimentary  environment or basin are typically surrounded  

by water in an aquatic environment where water  infiltrates pore spaces and becomes poor water  

and then reactions might occur that cause the  precipitation of cement in between those grains  

and that whole process causes the lithification or  rock formation of those grains and turns them into  

rocks but this is all sedimentary when it comes  to metamorphic rocks you have to get a little  

further down in the burial to really get the high  enough temperatures and pressures to cause the  

actual clastic grains in between the cement or  poor water to react with that cement in pore water  

and once they start to react and participate in  those reactions that is then termed metamorphism  

but that line is not super clear so sometimes  when you're right on the brink of it you'll see  

some overlap there on the other spectrum at high  temperatures rather than low temperatures melts  

can be generated from rock material that makes the  line between metamorphism and igneous processes a  

little bit fuzzy but we can also define this  line for example the melt that forms at these  

high temperatures cools or crystallizes to form  true igneous rocks whereas the residue that didn't  

fully melt is metamorphic metamorphic rocks  however can form in a variety of environments  

under a variety of conditions there are many  types of metamorphism for example we have regional  

and contact which are probably the most commonly  taught types of metamorphism regional metamorphism  

is obviously on a regional scale where subduction  zones or any plate boundaries for example  

are causing high temperatures and pressures of  rocks that are being buried and crushed underneath  

those plate boundaries and deformed but not fully  melted and those rocks that are becoming deformed  

in these high temperature pressure environments on  a regional scale are doing so by way of regional  

metamorphism whereas contact metamorphism is  when intrusions of magma chambers for example or  

plutons come up and come into contact with country  rock which that heat caused by that intrusion then  

metamorphosis right at that fuzzy contact shown in  this figure between the intrusion and the country  

rock and this contact metamorphism is typically  dominated by heating rather than pressure so we're  

not going to see the same textures as we would  in the rocks that were regionally metamorphosed  

because those had high pressures to orient the  mineral grains in a certain fashion whereas the  

contact metamorphism is heating not necessarily  pressure so it's not going to have as much  

orienting of grains and we'll see that when  we get to the metamorphic textures part of  

this video but there are many other types of  metamorphism other than regional contact which  

include burial for example in which the deep  burial of sediments can cause high temperature  

and pressures and therefore metamorphism just  like we talked about when it comes to the line  

between diogenesis and metamorphism we'll see this  in a couple slides when we talk about whether coal  

is an example of a metamorphic rock because it  really depends on the level of burial digenesis  

or burial metamorphism that occurred we also have  here dynamic metamorphism in which shear zones  

which are contacts between rocks that are sliding  against each other cause pressure and temperature  

enough to deform those rocks in that zone and  cause them to gain metamorphic characteristics  

and therefore it's metamorphism we also have  hydrothermal metamorphism up at the right corner  

here which is caused by the convection of really  hot hydrothermal fluid water through that upper  

oceanic newly formed crust water that convects  through those newly formed igneous minerals like  

feldspars and peroxides and amphiboles to react  with them and transform them into micas and clays  

and down here we have impact metamorphism  which is pretty self-explanatory from its  

name but it is the metamorphism caused by the  really really high temperatures and pressures  

upon impact of a meteorite and obviously this  is a really localized type of metamorphism but  

causes some really really specific and diagnostic  characteristic metamorphic textures so now that  

we've talked about what metamorphism is as  well as what types of metamorphism there are  

what is the goal of metamorphic petrology well we  have three major goals when studying metamorphic  

petrology the first is to determine the protolift  of the metamorphic rock that is the original  

rock before it became metamorphosed and if we  determine it to be igneous or sedimentary then  

what kind of igneous or sedimentary rock can  we draw any more conclusions other than just  

it being igneous or sedimentary and can that  tell us about maybe what kind of environment  

it underwent metamorphism in and maybe about the  type of metamorphism it underwent for example our  

next goal of studying metamorphic petrology is  to determine the conditions of the metamorphism  

and these are things like the temperature and  pressure the rock crystallized at the composition  

of the fluid present during metamorphism  because maybe that caused compositional changes  

to the protolith that caused it to become the  metamorphic rocket is at that point and did the  

rock change composition during metamorphism  which is basically what i just said did any  

fluids alter it did it change composition purely  because the higher temperatures and pressures  

caused it to there are a lot of things to  consider when looking at metamorphic rocks  

and the last major goal is determining  the structural history rather than just  

the compositional history so was the rock  structurally deformed did it deform before  

during or after metamorphism and basically  overall what can that tell us about the history of  

the rock so let's start with protolis how do  we determine a metamorphic rock's protolith  

well in many cases it's somewhat simple for  example marble is the metamorphic rock that  

forms when limestone undergoes metamorphism and  how do we know this well marvel's composition  

is completely calcitic it's made of calcite it's  just that the calcite grains have become deformed  

and recrystallized to form a really hard version  of calcite and limestone starts as also being  

the composition of calcite calcium carbonate so we  know marble's protolith because of its composition  

likewise quartzite typically has a sandstone  protolith why well quartzite's composition  

obviously from its name is dominated by quartz  and quartz grains are really common in sandstone  

many sandstones are dominated by quartz and when  sandstones undergo metamorphism the quartz grains  

typically dominate the recrystallization fabric  and become this really hard rock called quartzite  

you'll see a common theme here when we talk about  metamorphic rocks and that is they are harder  

than their sedimentary protoliths and that's  because they're becoming so densely packed  

and recrystallized under pressure and that causes  them to be much harder and if you don't know what  

mineral hardness is to begin with you can check  out this video up here linked to the top right i  

talk about mineral hardness and there and the mohs  hardness scale if you want to know the difference  

between the hardness of different minerals another  compositionally similar rock to its protolith  

is nice nice is a high grade metamorphic rock  meaning it underwent very high temperatures  

and pressures to become metamorphic that is  typically the metamorphic version of granite  

granite contains mostly quartz and feldspar  and sometimes amphiboles peroxines and micas  

and nice contains typically the same things and  becomes banded because of this compositional  

variation however as we'll see later nice is  not so simple and there are a few other ways  

or protolis in which metamorphism can cause this  type of metamorphic banding another example of  

metamorphic rock that is pretty easy to tell its  protolith is schist and slate schist is the high  

grade metamorphic rock to shale and slate is the  low grade metamorphic rock to shale shale is the  

protolith for both when only undergoing relatively  low temperature and pressure metamorphism shale  

becomes slate and when undergoing high temperature  and pressure metamorphism shale becomes schist or  

sleep becomes schist after it's already been met  morphosed and low-grade metamorphism you might  

think that the schist looks very shiny and very  different than boring old shale or clay but this  

chest is shiny because of all the mica minerals  that it contains like muscovite for example  

and these mica minerals form from their original  proto-lip clay minerals and so it's pretty easily  

recognizable to say that the proto-lithius was  some sort of clay mineral dominated rock basalt  

is a little bit more difficult basalt can be very  many different compositions so saying that basalt  

is the protolith to blank metamorphic rock is very  difficult because there's a lot of different types  

of basalt and so it has compositional variety it  has structural variety it has a lot of variety  

that makes its final metamorphic equivalent hard  to determine but a couple examples that we'll talk  

more later in the video about are green schist  and ecleggite which are two types of metamorphic  

rock that can result from different types of  basalt but it depends on both the original  

composition of the basalt and the metamorphic  grade of the metamorphism so if it's high grade  

it'll be different than if it's low grade etc the  last example i show here is coal so remember how  

we said coal is kind of on that fuzzy line between  diogenesis and metamorphism that is because coal  

forms by burial metamorphism and it's low grade  at that so relatively low temperate pressure for  

metamorphism and what we see is that vitamins  coal which technically is still sedimentary can  

metamorphose by low-grade barium anamorphism into  anthracite coal and so anthracite can sometimes  

technically be classified as metamorphic  because it's just past that fuzzy line of  

digenesis to metamorphism but again when we're  determining protolis anthracite is pretty simple  

obviously it's protolith it's cold we know that  because it's coal but what can we tell using the  

textures of metamorphic rocks yes we can look at  the compositions but until we really observe the  

textures in that metamorphic rock we can't tell  much more about its structural history and about  

the metamorphic environment that it formed in  without looking at the textures primary textures  

of rocks form during deposition of sedimentary  rocks or during crystallization of igneous rocks  

and these can sometimes be saved in metamorphic  rocks if it was relatively low grade metamorphism  

or the original rock was relatively sturdy and  preserved some of that primary texture during  

the metamorphism however metamorphic textures are  more so secondary and can be classified as either  

static textures or tectonics textures these are  exactly what they sound like static texture refers  

to minerals that grew or recrystallized without  deformation or after deformation and therefore  

aren't smushed or oriented in any regular pattern  whereas tectonic textures are those that grew or  

recrystallized during or before deformation and  therefore are smushed or foliated or some sort  

of pressure texture is observed in tectonic  textures or tectonically deformed metamorphic  

rocks so first let's talk about primary textures  and what might be preserved in metamorphic rocks  

and then we'll talk about the secondary  metamorphic textures that are added onto that  

and what we can glean from both of those types of  textures so sedimentary types of primary textures  

are things like bedding and sometimes bedding can  manifest as compositional layering in metamorphic  

rocks as we can see on the right here but like we  talked about this nice spanning or compositional  

banding can also be due to a granite protolith so  how do we tell between whether the nice layering  

or banding is due to a stratified sandstone for  example or a granite in general thin cortzos  

calcareous or politic layers politic is muddy or  clayey indicates a sedimentary protolith however  

many sedimentary textures are obliterated during  metamorphism so if it is low-grade metamorphism  

maybe they're still somewhat preserved but  if it's high grade and you can tell that  

then it's probably not sedimentary textures that  you're looking at it might be leftover igneous  

textures but it's probably more likely secondary  metamorphic or deformation textures oh and here's  

an example of nice banding just to get a contrast  there but moving on to igneous primary textures  

the most distinguishing relic igneous texture is  probably tabular feldspar so tabular plagioclase  

k feldspar indicates an ortho nice or an  igneous protolith nice over paranise or a  

sedimentary protolith mice some other types of  atheist primary textures that might be preserved  

in metamorphic rocks include pillow basalts  so pillow basalts often are metamorphosed by  

alteration or hydrothermal metamorphism like we  saw in the hydrothermal vent environment that the  

water altered the materials surrounding that  vent and pillow basalts sometimes have these  

rims of alteration that we can see on their outer  surfaces and in these pillow basalts they still  

maintained their igneous primary texture  of being pillow basalts but another type of  

igneous relic texture is vesicles so vesicles  form at the tops of lava flows typically  

and sometimes these vesicles during metamorphism  aren't completely obliterated and instead they're  

filled with minerals like zeolite calcite epitope  or pranite so if you see vesicles that are filled  

with little white minerals like this sometimes  that's an igneous relic texture that there were  

vesicles in the parent rock or protolith and that  indicates an igneous protolith although many times  

if pressure is involved in the metamorphism  those vesicles aren't preserved so what is  

most often preserved in metamorphic rocks  well not the primary textures it's typically  

the metamorphic textures or the secondary textures  caused by metamorphism because metamorphism often  

obliterates a lot of the primary textures so  what are these metamorphic textures or static  

and tectonic textures and how can we recognize  them well like i mentioned static textures  

are textures caused by minerals that grow without  deformation or after deformation and some terms  

we'll talk about are ideoblastic and granoblastic  whereas tectonic textures are those that show that  

the minerals obviously were deformed after they  grew and we can see foliation schistosity and  

delineation as well as nice acidity which we kind  of just talked about it's like nice expanding so  

we can see those in the pressure involved or  tectonic textures but we'll start with the static  

textures so static metamorphic textures are those  that arise from high temperature metamorphism  

but probably weren't put under as high of  pressure in their metamorphic environment for  

example something like contact metamorphism could  have caused them and in static textures grains are  

typically equint or equal in size another term for  this is equal granular we can see this over here  

to the right and also they have dihedral angles or  angles at which their brain boundaries meet that  

are around 128 degrees so we can see a lot of the  grain boundaries here have angles of 120 degrees  

and that is very typical of static metamorphic  textures and when euhedral crystals are present  

crystals with well-defined crystal faces the  texture is called ideoblastic however sometimes  

coarse-grained crystals in metamorphic rocks  can be present amongst a finer grained matrix  

of metamorphic minerals and these are called  porphyroblasts and these can include things like  

garnet starlight or alumina silicates granoblastic  textures as opposed to ideoblastic textures result  

from crystallization that occurs after deformation  one type of granoplastic texture is exhibited  

in the fine grained rock horn fells and the  inter-grown crystal network of horn fells another  

grand of blastic rocks often caused them to break  concoidally and we'll talk more about this in  

the classification slide at the end tectonic  metamorphic textures on the other hand develop  

a crystallographic preferred orientation however  there are different terms for different planar  

features and we'll talk about these terms  now so foliation is one example where  

it basically applies to anything that is a planar  feature in the rock schistosity on the other hand  

are planar features defined by preferred  orientation of platy or tabular minerals  

lineation on the other hand describes linear  rather than planar features so a line is a line  

a plane as a plane and linear features that formed  by preferential orientation of tabular minerals  

or by intersection of foliation planes so  we can see that this figure c example has  

lineation and foliation but no schistosity because  those minerals are aligned linearly because  

they're tabular they're not plenty whereas this  figure d has all three foliation systolicity and  

lineation we can see the linear tabular minerals  are aligned and then we have the plating minerals  

that are a parallel to betting orientation and  then we have the foliation in the center so  

all three are present in figure d and they're all  slightly different from one another lastly getting  

into classification so metamorphic classification  can be done using structural classification or  

structural terms or by compositional terms  so first let's talk about the structural  

terminology or structural classification of  metamorphic rocks then on the next slide we'll  

talk about compositional classification and  sometimes both of these types of terms can be  

used to describe a metamorphic rock so first  we have granofels here which is of course  

equal granular rock however if you are taking  metamorphic petrology i'll let you in on a secret  

here we never once had to identify granofels so  i'm not sure how important it is to you but we  

did talk a little bit more about hornfels which  is a much finer grained concoidally breaking rock  

which means it breaks with conchoidal fracture  kind of like glass or obsidian rather than along  

any defined crystallographic planes slate on  the other hand is a very fine-grained rock  

that does break along to find crystal graphic or  cleavage planes it's very similar to its protolith  

of shale in that it's platy and has these cleavage  planes but it's much harder than shale itself fill  

light is another very fine grained rock but it has  a silky luster as well as on its cleavage planes  

which distinguishes it from slate because yes it  has cleavage but it's got the silky luster it also  

in my opinion is not as platy as slate so if  you're trying to distinguish between the two  

it's more of a um it's platy but thinner thinner  plates in in in hand table it's hard to show  

without like holding one um schist is another  thing that i think a lot of people sometimes think  

is hard to distinguish from phyllite but until  i actually held a true fill light i agreed with  

this now i think it's relatively easy if you hold  and look at a fill light it's much less schistose  

if you hold a shift it's getting like kind of  flake off whereas if you hold a fill light it's  

not as flaky it's not as micacious it's a bit more  hard and held together in what you know i've held  

this is only all in my experience lastly nice here  is a lot different than all these other structures  

of metamorphic rocks and it's you know very hard  it's not going to flake anything and it's got this  

banding it's just really easily recognizable it  kind of just looks like a really banded granite  

but again these are just structural terms to get  into the compositional metamorphic terms we have  

to talk about these names so here are metamorphic  rock names that imply mineral assemblages rather  

than just structures green schist is the first one  listed here which is a foliated mafic metamorphic  

rock with actinilite as its major amphibole the  other thing here is green stone which is a massive  

mafic metamorphic rock which also has actinide  as its major amphibole and the only difference  

here is that one is foliated greenish and  one is massive and obviously the schist  

term at the interior of the green schist is a bit  more of a structural term and that refers to its  

foliation or viscosity whereas the massive rock  is obviously not just its stone because it doesn't  

have that foliation and schistosity that the grain  just has ample light is another i think is really  

easily recognized and that is a metamorphic rock  that is kind of like black and white polka dotted  

almost that is mavic with horn blend as a major  amphibole so if you know amphiboles are just kind  

of like dark igneous minerals and amphibolite is  kind of a mixture between you know it's got a lot  

of ampables but it's also got some felsic material  and so it's got this white and black dalmatian-y  

type of look with of course black being the  dominant because amphiboles are dominating its  

fabric and that's why it's called amphibolite the  next term here is blue chest bluishest is a mafic  

metamorphic rock with sodic amphibole as its  major amp so soda you know things like gameplay

which are blue in color giving blue just its  name and sodic just refers to these types  

of ambles being rich in sodium as opposed to  other common cations in these igneous minerals  

is a mafic metamorphic rock with orthopyroxene  and clinopyroxene as its dominant minerals now  

i'm going to let you in here on another secret  from when i talk metamorphic photology and that  

is i never had to identify granulite i don't  even really remember going over it so i'm not  

sure how important it will be for you to know  about the next one is ecleggite which i love  

because it's not only easy to recognize but also  really freaking beautiful a necklace is a mapic  

metamorphic rock with chloe peroxin and garnet  as its major minerals and the clano peroxine that  

it is dominated by is a green color and it makes  it this beautiful green with these beautiful red  

garnets in it and so eclectic it's just really  recognizable with it's green and it's garnet  

peripheral blasts in it and so it's just really  recognizable and beautiful not exactly type marble  

is the next one we already talked about protolith  being limestone and it's typically foley calcite  

and or dolomite and quartzite we also talked about  its protolith typically being sandstones or quartz  

rich sandstones and quartzite is obviously as  its name suggests dominated by quartz lastly  

serpentine is an ultra mafic metamorphic rock that  is dominated by serpentine so its major minerals  

name is the same as its rock name and again guys  what i remember most from metamorphic patrology  

is having to identify serpentine or sometimes  called serpentinite quartzite marble ecleggite  

amphibolite and then structures like nice schist  fill light and slate so that is all i have for  

today's introductory metamorphic petrology video  and to make this video i am using the essentials  

of igneous and metamorphic petrology by ronald and  carol frost if you want to check out this book it  

is linked in my description along with other minor  and supporting references and if you want to check  

out the other videos in this metamorphic petrology  playlist here's a couple upcoming videos in this  

playlist have listed here um but obviously  i haven't started them yet because they're  

just text here and they're not thumbnails yet but  you know maybe by the time you're watching this  

they're already out so if you want to see more  about metamorphic challenge you can click below  

in the rectangle below that says metamorphicology  playlist and see if those videos are out and with  

that i will let you guys go thanks so much for  watching and i'll see you guys next time bye