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. Found in the rocks slate and phyllite. During the earliest stages of low grade metamorphism, most pressure is from the weight of overlying rock. Therefore the new sheet structure minerals, such as clay, tend to parallel the bedding planes of the sedimentary rock being metamorphosed.
With folding the sedimentary clay layering folds with the rock so that the layering still runs parallel with the bedding planes. At this point the rock is still sedimentary. With deeper burial or under the influence of compression, metamorphism begins. The sedimentary clay minerals are converted into the mineral chlorite, that has flat basal cleavage like a mica. But the chlorite is growing in a stress field that is not always running parallel to the bedding.
In other words, sedimentary rocks with layering will have thin layers of coarse and fine sediments or fragments. Upon close observation, one will be able to notice marks, trace fossils and soft sediment deformation. To differentiate foliation and layering, let us begin with how they are formed. Foliation is based on the principle of stress while layering is caused by small mica fragments embedding on the rocks. Foliation is formed by fire and stress; layering is caused by thin embedding of both coarse and fine deposits.
Also, foliation is due to the alteration of minerals from heat and pressure. Foliation may be defined as a general planar structure resulting through parallel alignment of sheets of silicate material. The result is the banded appearance of the rock. Metamorphic rocks are formed by the transformation of existing rocks through the process of metamorphism. In the formation of metamorphic rock, the original rock is subjected to heat and pressure causing the rock to undergo physical and chemical changes.
Foliation means a pattern of penetration caused by the realignment of minerals like mica. It is also used to state the appearance of metamorphic rocks. So by the principle of stress direction, a product called metamorphic rock is formed. A close observation of the perpendicular formation has to be made to decipher the direction of the shortening.
It is formed by stress and fire. It is caused by an alteration of minerals from pressure and heat. Slate is a foliated metamorphic rock origination from shale through the process of foliation. Other examples are phyllite, schist and gneiss. The protolith for slate is shale, and sometimes fossils that were present in the original rock can be seen in freshly sheared layers of slate.
Composed of minerals that do not elongate or align during metamorphosis, nonfoliated metamorphic rocks tend to be simpler than foliated rocks. Examples of nonfoliated metamorphic rocks include marbles, quartzites and soapstones. Granofels is a broad term for medium- to coarse-grained metamorphic rocks that do not exhibit any specific foliation.
A hard rock that is easy to carve, marble is often used to make floor tiles, columns and sculptures. A very hard rock, quartzite is often used to make kitchen countertops and floor tiles.
Rich in talc, soapstones feel greasy, like soap. Soapstone is a relatively soft metamorphic rock and absorbs and holds heat well, so it is often used around fireplaces and woodstoves.
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