What does Aphanitic texture mean?

Aphanitic – This texture describes very fine grained rock where individual crystals can be seen only with the aid of a microscope, i.e. the rock is mostly groundmass. An aphanitic texture is developed when magma is erupted at the Earth’s surface and cools too quickly for large crystals to grow.

What has an aphanitic texture?

IGNEOUS ROCK TEXTURES

APHANITIC TEXTURE – Igneous rocks that form on the earth’s surface have very fine-grained texture because the crystals are too small to see without magnification.

What does it mean if an igneous rock has an aphanitic texture?

Aphanitic rock is igneous rock in which the grain or crystalline structure is too fine to be seen by the unaided eye. Such rock is formed when the material solidifies at or near the surface so that the cooling is rather rapid. Such rocks are termed “extrusive” rocks.

Does aphanitic mean?

[ ăf′ə-nĭt′ĭk ] Of or relating to an igneous rock in which the crystals are so fine that individual minerals cannot be distinguished with the naked eye. Aphanitic rocks are extrusive rocks that cooled so quickly that crystal growth was inhibited. Compare phaneritic.

What is aphanitic and pyroclastic texture?

There are six main types of textures; phaneritic, aphanitic, porphyritic, glassy, pyroclastic and pegmatitic. Aphanitic (a = not, phaner = visible) rocks, in contrast to phaneritic rocks, typically form from lava which crystallize rapidly on or near Earth’s surface.

What does aphanitic look like?

Aphanitic texture consists of small crystals that cannot be seen by the eye with or hand lens. The entire rock is made up of small crystals, which are generally less than 1/2 mm in size. This texture results from rapid cooling in volcanic or hypabyssal (shallow subsurface) environments.

What is aphanitic form?

aphanitic An igneous rock texture characterized by mineral grains which are too small to be identified without a petrological microscope. These extremely fine-grained, crystalline fabrics are formed when a magma solidifies in response to a very rapid loss of heat and dissolved gases.

What does the term aphanitic mean quizlet?

Aphanitic. Fine-grained, with crystals too small to identify without a microscope.

How do you identify aphanitic rocks?

Aphanitic igneous rocks have a fine-grained texture and most of their crystals are too small to see with the naked eye. You will need to use a magnifying glass to observe the crystals in aphanitic rocks. Igneous rocks that form too quickly for crystals to form have what is called a glassy texture.

What do aphanitic and Phaneritic textures look like and what do they tell us about the way the rock formed?

In aphanitic rocks, the crystals are large enough to be identified with the naked eye, while in phaneritic rocks they are not. b. Phaneritic rocks cool slowly, and therefore have small crystals, while aphanitic rocks have large crystals and cool quickly.

How are phaneritic and aphanitic different?

Rocks that are aphanitic have a grain size below 1 millimetre. On the other hand, phaneritic rocks have grains that are coarse and the grain size is usually between 1 millimetre and 10 millimetres.

Is gabbro an aphanitic?

Gabbro is distinct from anorthosite, which contains less than 10% mafic minerals. Coarse-grained gabbroids are produced by slow crystallization of magma having the same composition as the lava that solidifies rapidly to form fine-grained (aphanitic) basalt.

What do all the rocks that are aphanitic have in common?

Aphanites are commonly porphyritic, having large crystals embedded in the fine groundmass, or matrix. The larger inclusions are called phenocrysts. They consist essentially of very small crystals of minerals such as plagioclase feldspar, with hornblende or augite, and may contain also biotite, quartz, and orthoclase.

What does it mean if an igneous rock has an Aphanitic texture quizlet?

What does it mean if an igneous rock has an aphanitic texture? The igneous rock exhibits mineral crystals too small to see with the naked eye.

Where are pegmatite rocks found?

Pegmatite is found in all over the world. They are most abundant old rocks. Some are found in large intrusive igneous rocks, while others are scattered over rocks surrounding intrusive magmatic rocks. Worldwide, notable pegmatite occurrences are within the major cratons, and within greenschist-facies metamorphic belts.

Which of the following igneous rocks exhibit Aphanitic texture?

Basalt is the aphanitic or fine-grained equivalent of gabbro.

What is the aphanitic equivalent of gabbro?

Basalt

Basalt is the aphanitic (fine-textured) extrusive equivalent of gabbro. From the Latin word “pumex”, meaning “pumice”. A vesicular, glassy volcanic rock, generally of rhyolite composition (felsic). Often light in color.

What type of igneous rock consists of very coarse crystals?

intrusive, igneous

If the magma stays inside the earth and takes thousands of years to cool, it has time to make big crystals. These crystals make a coarse-grained igneous rock called plutonic, or intrusive, igneous rock because the magma was intruded into cracks deep under the earth’s surface.

What rocks are composed almost entirely of light colored silicates?

ES Chapter 03 Vocabulary Review

What color is silicate?

The silicate minerals containing iron and magnesium are generally dark-colored (dark green, gray, or black) and are referred to as mafic (or ferromagnesian) minerals. Plagioclase feldspars may range from pale-colored sodium-rich varieties (such as albite), to darker grey, calcium-rich varieties (such as labradorite).

What are silicate rocks?

Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth’s crust. In mineralogy, silica (silicon dioxide) SiO ₂ is usually considered a silicate mineral.

What is peridotite chemical composition called?

doʊˌtaɪt, pəˈrɪd. ə-/ PERR-ih-doh-tyte, pə-RID-ə-) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica.

What is peridotite texture and composition?

Peridotite

Is peridotite a texture?

Peridotite is the general name for the ultrabasic or ultramafic intrusive rocks, dark green to black in color, dense and coarse-grained texture, often as layered igneous complex.

What is basalt texture?

Basalts show, almost always, aphanitic or fine-grained mineral texture resulting from rapid cooling of volcanic magma on or close to the surface of Earth. The component minerals are so fine that cannot be identifiable by the unaided eyes.

What type of aphanitic texture does olivine basalt have?

The individual crystals in phaneritic texture are readily visible to the unaided eye. Figure 4.1. 1: Basalt is a classic fine-grained (aphanitic) extrusive igneous rock. This sample is mostly fine groundmass with a few small green phenocrysts that are the mineral olivine.

What is the texture of dacite?

Dacite (/ˈdeɪsaɪt/) is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite.