Two common non-foliated metamorphic rocks are marble and quartzite. Identify quartzite by its pale or translucent color. If the rock has a pale color to it that is almost see-through in some areas, it may be quartzite.
Quartz crystals are almost clear, and they tend to stay that way after metamorphosis. See if the rock is gneiss by checking for light and dark bands. Bands or foliations that seem almost perfectly black and white are indicative of gneiss. Gneiss is composed of clear quartz and darker crystals, leading to remarkably differentiated striations. Less distinguishable bands suggest that the rock may be another kind.
Scratch the rock against a glass bottle to determine its softness. Gently streak the rock against glass that you are holding firmly in place. Gneiss and quartzite, however, can both scratch glass with very little force. Identify marble by looking for grains that seem to have no pattern. Marble can vary widely in color, but the most common colors are white and grey. Check whether the rock is slate by looking for flat sheet layers.
You should be able to see the clearly divided sheets within the rock itself, which are considered foliations, though they do not look like the bands in gneiss. Distinguish phyllite from slate by checking for visible crystals and a green hue. Crystals in slate are too small to see with the naked eye, while phyllite has a grainier appearance, though it still has layers like slate.
In addition, you may notice a deeper green hue in phyllite than you would find in slate, though not all phyllite is green. Include your email address to get a message when this question is answered. Measure ad performance. Select basic ads. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products.
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Igneous Rock Identification. The layering produces three distinctly different looking rocks, those with slaty cleavage e. Metamorphic rocks are identified on these textures click image for large version, or go to Metamorphic Texture for more details.
One source of confusion is that we have both texture names and rock names, and although they often refer to the same thing, there are exceptions. The table below shows all the relationships. Since texture names and rock names do not line up perfectly it is important to distinguish them, but from this point on we will refer to everything by rock names. Metamorphic Rock Composition Metamorphism is the alteration of a parent rock into a metamorphic rock.
There are as many parent rocks as there are igneous, sedimentary, and metamorphic rocks, since any of these can be metamorphosed. But, the simplest way to examine compositional changes during metamorphism is to start with the three end products of the simple model for sedimentary rocks , shown in the illustration below click picture for full model.
These weathering products are also the most common sedimentary rocks and form a very large percentage of the metamorphic rocks we see. These three end products attractors in the sedimentary model quartz sandstone , shale , and limestone become the three parent rocks of metamorphism. All the metamorphic rocks discussed here, and included in the identification key see below come from these three parents.
The Changes We See Compositionally simple sedimentary rocks, such as quartz sandstone and limestone calcite do not change composition with metamorphism - their chemistry is too simple. Quartz remains quartz, and calcite remains calcite. The rocks do recrystallize, though, forming granular rocks with fused grains; the rocks quartzite and marble. It does not matter by what process you metamorphose quartz sandstone and limestone, their composition does not change, and they produce the same kind of metamorphic rock.
Rocks with a more complex chemical composition, such as shale the mineral clay , however, undergo many compositional, and textural changes. They do not have layers of material. Schist is a layered metamorphic rock. Identify the chemical reactions that create some metamorphic rocks. For example, rocks changed by the ocean or in the ocean will have salt in them. They are also identified by the amount of water and other minerals found in them.
Look at the way the grain are formed. In schist rocks, you can see that the layers and the grains all go the same way. See the new forms caused by heat. There are many different types of metamorphic rocks depending on the amount of heat or pressure. Look at the type of change in the rocks and how the rocks melted from a heat source. One indication of metamorphism is the proximity to an erupted volcano. The heat from the magma can change rocks in the vicinity.
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