What kind of metamorphism changed the limestone to marble

Slate tends to break into flat sheets. Phyllite is similar to slate, but has typically been heated to a higher temperature; the micas have grown larger and are visible as a sheen on the surface. Where slate is typically planar, phyllite can form in wavy layers. In the formation of schist, the temperature has been hot enough so that individual mica crystals are visible, and other mineral crystals, such as quartz, feldspar, or garnet may also be visible.

In gneiss, the minerals may have separated into bands of different colours. In the example shown in Figure 7. 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. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

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You cannot download interactives. Igneous rocks are one of three main types of rocks along with sedimentary and metamorphic , and they include both intrusive and extrusive rocks. Sedimentary rocks are one of three main types of rocks, along with igneous and metamorphic. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image Metamorphic Rock Isua Metamorphic rock, estimated to be as old as 3.

Photograph by James L. This specimen is a piece of white marble with a large red ruby crystal from Afghanistan.

The transformation of limestone into marble usually occurs at convergent plate boundaries where large areas of Earth's crust are exposed to the heat and pressure of regional metamorphism.

Some marble also forms by contact metamorphism when a hot magma body heats adjacent limestone or dolostone. This process also occurs at convergent plate boundaries. Before metamorphism, the calcite in the limestone is often in the form of lithified fossil material and biological debris.

During metamorphism, this calcite recrystallizes and the texture of the rock changes. In the early stages of the limestone-to-marble transformation, the calcite crystals in the rock are very small.

In a freshly-broken hand specimen, they might only be recognized as a sugary sparkle of light reflecting from their tiny cleavage faces when the rock is played in the light. As metamorphism progresses, the crystals grow larger and become easily recognizable as interlocking crystals of calcite.

Recrystallization obscures the original fossils and sedimentary structures of the limestone. It also occurs without forming foliation, which normally is found in rocks that are altered by the directed pressure of a convergent plate boundary.

Recrystallization is what marks the separation between limestone and marble. Marble that has been exposed to low levels of metamorphism will have very small calcite crystals.

The crystals usually grow in size and as the level of metamorphism progresses. Clay minerals within the marble will alter to micas and more complex silicate structures as the level of metamorphism increases. Some might contribute to the formation of gem minerals such as corundum - the mineral of ruby and sapphire.

Marble Dimension Stone: Marble cut into blocks and slabs of specific size is known as "dimension stone. Marble occurs in large deposits that can be hundreds of feet thick and geographically extensive. This allows it to be economically mined on a large scale, with some mines and quarries producing millions of tons per year.

Most marble is made into either crushed stone or dimension stone. Crushed stone is used as an aggregate in highways, railroad beds, building foundations, and other types of construction.

Dimension stone is produced by sawing marble into pieces of specific dimensions. These are used in monuments, buildings, sculptures, paving and other projects. We have an article about " the uses of marble " that includes photos and descriptions of marble in many types of uses.

Gray Marble: This specimen has calcite cleavage faces up to several millimeters in size that are reflecting light. The specimen is about two inches five centimeters across. Calcium carbonate medicines: Marble is composed of calcium carbonate.