For the last month of my Petrology(study of rocks)class, I have been researching a garnet silliminite gneiss from Whitehall, NY. For the first part of the project, I had the oppurtunity to create a microscope slide of the rock, called a thin section. It involved cutting off the face of a 5"x10" sample,then cutting it to 1/2 an " in thickness with a straight saw blade. I then used a circular saw to cut it to the dimensions of a slide. Next I epoxied it to the slide and used the blade to shave it down to about 1/16th of an inch. I then spent ~4 hrs. sanding it with carbide grit and water.( After this process I don't think any of the students will ever drop a pre-made slide again 
)It had to be the thickness of a hair, because when viewing it in plan polarized light under a microscope if it is too thick you will get the wrong interference colors. Interference colors are due to the composition and structure of different minerals in the rock and help tell us what type of rock we are looking at. Each type of mineral will give a certain interference
color. We also look for different textures and alterations to learn about the formation of the rock.Anyway I figured I'd prep you for some pics. After creating the slide and determining different minerals, textures etc. We went on a series of fieldtrips. The project culminated with a power point presentation and paper about the rock's petrology and tectonic setting. I brought my road atlas on the field trips and marked down some nice cellar holes as well as a prospective spot to find trilobite fossils. Tomorrow I will finish my last lab and have a break from school work for a few weeks. I plan on doing some detecting also!
pic 2 is an altered garnet, it remains black in polarized light
pic 3 is a garnet with pyrite, due to the size it is termed a porphyroblast
pic 4 is a sheared garnet or augen. The white minerals have intruded it and are orthoclase, plagioclase and quartz
pic 5 is an orthoclase(feldspar) porphyroblast(you can tell it from quartz by the sharp angled cleavage
pic 6 is a slickenside, theswe occur in areas of faulting where on rock slides against another
)It had to be the thickness of a hair, because when viewing it in plan polarized light under a microscope if it is too thick you will get the wrong interference colors. Interference colors are due to the composition and structure of different minerals in the rock and help tell us what type of rock we are looking at. Each type of mineral will give a certain interferencecolor. We also look for different textures and alterations to learn about the formation of the rock.Anyway I figured I'd prep you for some pics. After creating the slide and determining different minerals, textures etc. We went on a series of fieldtrips. The project culminated with a power point presentation and paper about the rock's petrology and tectonic setting. I brought my road atlas on the field trips
and marked down some nice cellar holes as well as a prospective spot to find trilobite fossils. Tomorrow I will finish my last lab and have a break from school work for a few weeks. I plan on doing some detecting also!pic 2 is an altered garnet, it remains black in polarized light
pic 3 is a garnet with pyrite, due to the size it is termed a porphyroblast
pic 4 is a sheared garnet or augen. The white minerals have intruded it and are orthoclase, plagioclase and quartz
pic 5 is an orthoclase(feldspar) porphyroblast(you can tell it from quartz by the sharp angled cleavage
pic 6 is a slickenside, theswe occur in areas of faulting where on rock slides against another