What Does Aphanitic Mean

What does the word aphanitic mean?

Aphanitic is a descriptive term for small crystals and phaneritic for larger ones. … aid of a microscope (called aphanitic from the Greek aphanēs meaning “invisible”) or contains no minerals at all (in the latter case the rock is composed of glass which is a highly viscous liquid).

What does Aphanitic texture mean?

fine grained

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 does the term porphyritic mean?

Definition of porphyritic

1 : of or relating to porphyry. 2 : having distinct crystals (as of feldspar) in a relatively fine-grained base.

What does felsic stand for?

Felsic refers to silicate minerals magma and rocks which are enriched in the lighter elements such as silicon oxygen aluminium sodium and potassium. Felsic magma or lava is higher in viscosity than mafic magma/lava. Felsic rocks are usually light in color and have specific gravities less than 3.

How do you pronounce Aphanitic?

Is quartz an Aphanitic?

Aphanites are commonly porphyritic having large crystals embedded in the fine groundmass or matrix. … 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 Aphanitic texture 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.

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What is an aphanitic igneous rock?

The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. Examples of aphanitic igneous rock include basalt andesite and rhyolite. Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur.

What is the opposite of aphanitic?

Aphanitic (a = not phaner = visible) rocks in contrast to phaneritic rocks typically form from lava which crystallize rapidly on or near Earth’s surface. When extrusive rocks make contact with the atmosphere they cool quickly so the minerals do not have time to form large crystals.

Does obsidian exist?

obsidian igneous rock occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes. Obsidian is extremely rich in silica (about 65 to 80 percent) is low in water and has a chemical composition similar to rhyolite.

What rock is glassy?

volcanic glass any glassy rock formed from lava or magma that has a chemical composition close to that of granite (quartz plus alkali feldspar). Such molten material may reach very low temperatures without crystallizing but its viscosity may become very high.

How fast do porphyritic rocks cool?

Porphyritic:a mixture of large and small crystals – perhaps a two-stage cooling history with the large crystals (the phenocrysts) cooling slowly and the small crystals (the groundmass) cooling more quickly.

What is felsic lava?

Felsic lavas are low temperature lavas because lower temperatures are required to keep felsic minerals molten (and if it was hotter it would have incorporated more iron and magnesium in comparison to silica). … So mafic lavas are hot low in silica and volatiles and have relatively low viscosity.

What is another word for felsic?

Rocks with greater than 90% felsic minerals can also be called “leucocratic” meaning ‘light-coloured’.

What is felsic and mafic?

In a widely accepted silica-content classification scheme rocks with more than 65 percent silica are called felsic those with between 55 and 65 percent silica are intermediate those with between 45 and 55 percent silica are mafic and those with less than 45 percent are ultramafic.

How can we say that a rock is Aphanitic?

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.

What is the difference between Aphanitic and Phaneritic 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. PHANERITIC TEXTURE – Igneous rocks with large visible crystals because the rock formed slowly in an underground magma chamber.

How do you say pegmatites?

What is the composition of Aphanitic?

Aphanitic extrusive igneous rocks therefore have coarse-grained intrusive counterparts with the same chemical and mineral composition. … Both rock types are composed mainly of the silicate minerals quartz and orthoclase feldspar but the crystals in the rhyolite are too small to see without a microscope.

Is there olivine in granite?

Olivine is typically with pyroxenes (in basalt for example) and quartz + K-feldspar with micas (biotite and muscovite) is a typical composition of granite. … Olivine is a common rock-forming mineral in mafic and ultramafic igneous rocks but it also occurs in impure metamorphosed carbonate rocks (picture below).

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What rock is intrusive?

intrusive rock also called plutonic rock igneous rock formed from magma forced into older rocks at depths within the Earth’s crust which then slowly solidifies below the Earth’s surface though it may later be exposed by erosion. Igneous intrusions form a variety of rock types.

How do pyroclastic rocks form?

Pyroclastic rocks are rocks formed by accumulation of material generated by explosive fragmentation of magma and / or previously solid rock during the course of a volcanic eruption.

Where are pegmatite rocks found?


The hard rock minerals pegmatite and spodumene are found mainly in Australia. Read Lithium Mining Today May Influence What You Drive In the Future to learn more about lithium extraction and other potential sources of lithium.

What is a Phenocrysts in geology?

A relatively large crystal embedded in a finer-grained or glassy igneous rock. The presence of phenocrysts gives the rock a porphyritic texture (see illustration). Phenocrysts are represented most commonly by feldspar quartz biotite hornblende pyroxene and olivine.

Which samples contain fossils?

Mudstone shale and limestone are examples of sedimentary rock likely to contain fossils. As the layers of sediment build up on top of one another they create a physical timeline. The oldest layers along with the organisms that were fossilized as they formed are deepest. The youngest layers are found at the top.

What is pegmatite texture?

A pegmatitic texture is one in which the mineral grains are exceptionally large. This texture is found in intrusive rocks. … The extra large size does not mean that they cooled extra slowly. Instead the large crystals of a pegmatite formed in a magma that was extra rich in dissolved water.

What type of rock is obsidian?

Rondi: Everyone meet Obsidian an igneous rock that from melted rock or magma. Obsidian is an “extrusive” rock which means it is made from magma that erupted out of a volcano. If it was an igneous rock that formed from magma underground and did not erupt it would have been called an “intrusive” rock.

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What are the 4 different textures of igneous rocks?

Igneous Rock Textures
  • COARSE GRAINED TEXTURE (PHANERITIC) mineral grains easily visible (grains several mm in size or larger)
  • B) FINE GRAINED TEXTURE (APHANITIC) mineral grains smaller than 1mm (need hand lens or microscope to see minerals)

Where do you find peridotite?

Peridotite is the dominant rock of the upper part of Earth’s mantle. The compositions of peridotite nodules found in certain basalts and diamond pipes (kimberlites) are of special interest because they provide samples of Earth’s mantle brought up from depths ranging from about 30 km to 200 km or more.

Why is obsidian so dark?

Obsidian is commonly a translucent dark brown or black. Unlike basalt obsidian’s dark color is due to high amounts of impurities rather than the presence of dark colored minerals. The color of obsidian depends on the chemical composition of the impurities.

Is purple obsidian real?

Purple Obsidian naturally speaks to the psychic abilities within us. … Purple Obsidian is a see-through purple stone that can be purely purple and resemble amethyst may be clear with purple stripes or clear with purple freckles. These are very light purple specimens. You will receive one stone approximately 1″ – 1.25″.

Is obsidian sharper than diamond?

Surprising Things about Obsidian

Surprisingly the edge of a piece of obsidian is superior to that of a surgeon’s steel scalpel. It is 3 times sharper than diamond and between 500-1000 times sharper than a razor or a surgeon’s steel blade resulting in easier incisions and fewer microscopic ragged tissue cuts.

Can lava turn into glass?

Lava coming in contact with water will cool it quickly. In this case the chemical reaction causes the lava to turn into a type of igneous rock that is uncrystallized—just like glass. … This glass created by lava can come in many forms the most popular being pumice or obsidian.

Which is the only rock that can float on water?

The volcanic rock is called ‘pumice stone‘ and is very lightweight meaning it can float on water. Pumice is made when magma from a volcano cools really quickly in water.

What does aphanitic mean?

Aphanitic Meaning

What is the meaning of the word APHANITIC?

Igneous Rock Textures

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