Metamorphic Rocks Part 1: Metamorphic Changes When rocks are compressed and heat
ID: 114515 • Letter: M
Question
Metamorphic Rocks Part 1: Metamorphic Changes When rocks are compressed and heated within Earth, they change, or metamorphose. During metamorphism, rocks tend to change in the following ways minerals change into different, more stable minerals minerals grow larger flat minerals align themselves parallel to each other 1) Examine the photos below. Describe one or two observations how the minerals in these rocks changed during metamorphism metamorphis Jessica Smay John GrotzingerRamon Rivera- MoretHarvard Mineralogical Museum Part 2: Metamorphic Grades During metamorphism, the temperature of and pressure on a rock determine what the rock looks like If the temperatures and pressures are not very different from those on the surface of Earth (low- grade metamorphism), the minerals do not change much and are small In high temperatures and pressures (high-grade metamorphism), the minerals in a metamorphic rock change a lot, so they grow large and tend to form into dark and light bands Jessica Smay Schist Slate 2) List the rocks above in order from low-grade 1to high-grade metamorphic rocks Low grade 3) Describe what slate would look like if it was metamorphosed more Gneiss High grade oW. H. FREEMAN AND COMPANY LECTURE TUTORIALS FOR INTRODUCTORY GEOSCIENCE 45Explanation / Answer
1. By careful observation of the given two figures, it can be saide that
a. The minerals became elongated during metamorphism and
b. The felsic(light colored) and the mafic(dark colored) minerals are seperated into layers or band.
2. Low grade -> Slate Schist Gneiss -> High grade
Low grade to high grade is showing from slate to gneiss through schist.
3. If shale was metamorphosed more it woul look like phyllite, slightly higher grade of slate.
4.I totally agree with student 1 because if will never become smaller grained due to pressure. During metamorphism, grade is incresing and hence the effect of temperature is more than pressure. So it will form schist. Student 3 is also wrong because after reaching the highest degree of metamorphism the rock again started melting and as slate is the first form of metamorphism so it will keep changing its form only.
5. I agree with student2 because during metamorphism minerals grow due to both temperature and pressure. High temperature allows atoms to freely migrate and high pressure causes solution of cystals within the rock at their contact point.
6. Both the clay and mica belong to sheet sillicate. Due to greater temperature and pressure clay minerals become elengated and compressed and form cystalline mineral mica.
7. After reaching the highest grade of metamorphism, the rocks started to melt again. This condition forms a different type of rock which is called Migmatite. This rock is considered as a mixture of igneous and metamorphic rock. Thus, if a rock is melted, it would not be considered as metamorphic rock.