Why do igneous rocks have different textures?
Porphyritic Rocks the two images below show a hand sample and a thin section of porphyritic aphanitic textured rocks. Impact of this question views around the world. Ophitic texture - laths of plagioclase in a coarse grained matrix of pyroxene crystals, wherein the plagioclase is totally surrounded by pyroxene grains.
Thus, many rocks identified as gabbro in hand sample were subsequently classified as gabbronorite after thin section examination. In other words, they display two distinctive sizes of grains that are visible to the naked eye. Modal variations are described as normal if mafic minerals are more abundant at the bottom and as reversed if mafic minerals are more abundant at the top.
Hyalopilitic texture - a texture wherein microlites of plagioclase are more abundant than groundmass, and the groundmass consists of glass which occupies the tiny interstices between plagioclase grains. Namespaces Article Talk. Amygdular - if vesicles have been filled with material usually calcite, chalcedonay, or quartz, then the term amygdular should be added to the textural description of the rock.
Alteration codes. If you examine a fragmental volcanic rock closely you can see why. Two stages of cooling, i.
Dry and saturated NCR. Related questions What is basalt? If a rock partially melts, what is the composition of the first melt to form mafic or felsic?
This texture is found in granites.
Why do igneous rocks have different textures? Socratic
Vesicular - if the rock contains numerous holes that were once occupied by a gas phase, then this term is added to the textural description of the rock.
The spectral resolution of the EDS corresponds to that of an scanning electron microscope and lies, in average, at eV. The particular detector technology was derived from the development of the Mars APXS spectrometer for the Sojourner and Pathfinder missions. Igneous rocks are also classified according to their textures.
Based on the position of the red line in Figure 3. In a rock with a phaneritic texture, where all grains are about the same size, we use the grain size ranges shown to the right to describe the texture:. At high degrees of undercooling, both the growth rate and nucleation rate will be low.
The Texture of Igneous Rocks
Adam Bede has been added to your Reading List! What determines igneous rock texture? Petrology Prof. Tarbuck and F. Each kind of texture has a variety of different characteristics that make them unique. Why are the crystals so small or non-existent in some extrusive igneous rocks? Rock Cycle Notes. This is similar to carbonated beverages which are bottled at high pressure. Why do igneous rocks have crystals? Porphyritic textures develop when conditions during cooling of a magma change relatively quickly.
Even in intervals of glassy basaltic composition rocks, if chilled margins or intrusive contacts were recognized the rocks were classified as diabase.
Textures of Igneous Rocks
Equant grains are those with boundaries of equal lengths; rectangular tablet shapes are known as tabular grains; acicular grains are slender crystals; long fibers are known as fibrous grains, and a grain that is prismatic is one that has different types of prisms. Add to collection s Add to saved. The last textural term is reserved for pyroclastic rocks, those blown out into the atmosphere during violent volcanic eruptiions. For consistency, qualitative measurements especially the selection of igneous contacts were made by the entire team.