Rocks and minerals: Metamorphic rocks 2.1.4
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|(a)||metamorphisim as a solid state isochemical process that changes the characteristics of rock
||To include contact, dynamic and regional
|(b)||how the mineralogy and fabric of metamorphic rocks can be used to infer the composition of the parent rock
||To include the formation of:
|(c)||how as the intensity of metamorphism changes different minerals form which can be used to reconstruct the conditions of metamorphism.
||To include: metamorphic grade, index minerals|
Learners are likely to come to have some understanding as to what metamorphism is from previous studies, they may be able to suggest locations where metamorphism could happen, name some examples of metamorphic rocks and comment on why it happens. The idea that it is a solid state isochemical process could be related to previous scientific studies. Learners will then go on to consider how the story of the metamorphic rock can be inferred from the texture and composition of a metamorphic rock, how the temperature and pressure conditions can be suggested and evidence of the original rock. Following this learners will investigate the sequence of metamorphic minerals which can signpost to the metamorphic conditions.
Common misconceptions or difficulties students may have:
The main challenges here are likely to come from the introduction of unfamiliar terminology from rock types and index minerals and in naming textures, to support this learners could be given plenty of opportunity to use these new terms in describing hand specimens and photographs and in interpreting data on metamorphic conditions.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course:
General ideas about temperature and pressure conditions in different settings arises throughout the course, metamorphism is a particular focus in metamorphic petrology 5.4 where learners consider mineral stability in detail along with formation of metamorphic fabrics.
A simple introduction to this section could be the RSC metamorphism activities, there are 3 short activities, the first looks at simulating contact metamorphism, the second looks at the formation of slate and the third considers the deformation of fossils. Using this as a basic introduction learners could be introduced to the definition of metamorphism and how it is possible in contact, regional and dynamic settings.
Learners could then be introduced to a wide range of metamorphic rocks by means of hand specimens, photographs and the virtual microscope programme, learners could focus their observations on similarities, differences and the distinguishing features of each type. With experience of the rock types learners will take on the classification of metamorphic rocks using texture and mineralogy and be able to use this information to suggest the original sedimentary rock type.
The use of minerals to reconstruct conditions of formation is introduced next, learners may need support in visualising how minerals change in response to conditions. Learners can work through the linked activity (metamorphic grade exercise) to support their understanding on the range of conditions that can exist and how products give evidence for metamorphic setting.
Learners can begin to familiarise themselves with the rocks mentioned on the specification and identify their defining features.
Using the explore section of the virtual microscope site metamorphic rocks can be selected along with UK virtual microscope to narrow the search further.
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