What is the difference between sedimentary layering and metamorphic banding

If you zoom in for a close view of the marble in Figure These rocks are also of economic importance; marble and quartzite are used for dimension stone in buildings and for countertops in many homes. Furthermore, marble is commonly used for statues and sometimes grave markers. One final non-foliated rock type that should be mentioned is anthracite coal Figure As you may recall, coal is a sedimentary rock composed of fossilized plant remains. This sedimentary coal is called bituminous coal; under higher temperatures and pressures bituminous coal can lose more of the volatiles typical of coal water vapor, for example , but the carbon content is enriched, making metamorphic coal anthracite coal a hotter burning coal due to the higher carbon content.

Anthracite coal can be distinguished from sedimentary coal by the shinier appearance, and is somewhat harder than bituminous coal, although both coal types are of low density due to their carbon content. Note that this particular metamorphism is not a recrystallization event, per se, as coal is mostly organic remains. However, bonds are still being broken and reforming due to changes in temperature and pressure.

In order to identify and name metamorphic rocks, a logical first step would be to examine the rock for evidence of any pattern or foliation, and if present, identify what mineral or minerals are making the foliation pattern. Non-foliated metamorphic rocks can be identified by the properties defined by their mineral composition.

Below is a table summarizing the metamorphic rock types, foliation names, and protolith rock types Table Foliated Metamorphic Rocks As mentioned previously, differential pressures can cause a foliation to develop in metamorphosed rocks. Non-Foliated Metamorphic Rocks The other class of metamorphic rocks is non-foliated; the lack of foliation may be due to a lack of differential pressure involved in the metamorphic process.

Table Shale Slate Contains shiny muscovite light or biotite dark micas, may see other minerals. Has schistose pattern of foliation. Most gneiss has little or no mica because it forms at temperatures higher than those under which micas are stable. Unlike slate and phyllite, which typically only form from mudrock, schist, and especially gneiss, can form from a variety of parent rocks, including mudrock, sandstone, conglomerate, and a range of both volcanic and intrusive igneous rocks.

Schist and gneiss can be named on the basis of important minerals that are present. For example a schist derived from basalt is typically rich in the mineral chlorite, so we call it chlorite schist. One derived from shale may be a muscovite-biotite schist, or just a mica schist, or if there are garnets present it might be mica-garnet schist. Similarly, a gneiss that originated as basalt and is dominated by amphibole, is an amphibole gneiss or, more accurately, an amphibolite.

If a rock is buried to a great depth and encounters temperatures that are close to its melting point, it will partially melt.

The resulting rock, which includes both metamorphosed and igneous material, is known as a migmatite Figure 7. JPG] As already noted, the nature of the parent rock controls the types of metamorphic rocks that can form from it under differing metamorphic conditions. The kinds of rocks that can be expected to form at different metamorphic grades from various parent rocks are listed in Table 7.

Some rocks, such as granite, do not change much at the lower metamorphic grades because their minerals are still stable up to several hundred degrees. Metamorphic rocks that form under either low-pressure conditions or just confining pressure do not become foliated.

In most cases, this is because they are not buried deeply, and the heat for the metamorphism comes from a body of magma that has moved into the upper part of the crust.

This is contact metamorphism. Some examples of non-foliated metamorphic rocks are marble , quartzite , and hornfels. There is no need to resubmit your comment. Notify me of followup comments via e-mail. Written by : Nimisha Kaushik. User assumes all risk of use, damage, or injury. You agree that we have no liability for any damages. Foliation Foliation is a penetrating pattern formed in the metamorphic rocks. Summary: Foliation is developed by stress and fire while layering is developed by the embedding of fine and coarse deposits.

Foliation has layers while layering contains marks on them. Author Recent Posts. Nimisha Kaushik. Latest posts by Nimisha Kaushik see all. Help us improve. The sheets orient themselves perpendicular to the direction of maximum stress.

The new parallel mineral flakes produce a planar texture called foliation. Foliation can be subtle or pronounced depending on the degree of metamorphism. The foliated textures develop in the sequence listed below as temperature and pressure increases. Here we just define the textures. Below are descriptions and illustrations of how each texture develops. Slaty cleavage - a pervasive, parallel foliation layering of fine-grained platy minerals chlorite in a direction perpendicular to the direction of maximum stress.

Produces the rocks slate and phyllite. Schistosity - the layering in a coarse grained, crystalline rock due to the parallel arrangement of platy mineral grains such as muscovite and biotite. Other minerals present are typically quartz and feldspar, plus a variety of other minerals such as garnet, staurolite, kyanite, sillimanite.

Mineral Banding Gneiss - The layering in a rock in which bands or lenses of granular minerals quartz and feldspar alternate with bands or lenses in which platy mica or elongate amphibole minerals predominate.

Page of all texture development illustrations Slaty Cleavage A pervasive, parallel foliation layering of fine-grained platy minerals chlorite in a direction perpendicular to the direction of maximum stress.