Aplite

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Aplite

Aplite in petrology

Petrology

In geology, petrology is the study of Rock s, and the conditions in which they form. Lithology once was approximately synonymous with petrography, but in current usage, lithology is a subdivision of petrology focusing on macroscopic hand-sample or outcrop-scale description of rocks, while petrography is the speciality that deals with m...
, the name given to intrusive

Intrusion

In geology, an intrusion is a body of igneous rock that has crystallized from molten magma below the surface of the Earth. Bodies of magma that solidify underground before they reach the surface of the earth are called plutons, named for Pluto , the Roman mythology of the underworld....
rock

Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
in which quartz

Quartz

Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
and feldspar

Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's Crust .Feldspars crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock....
are the dominant mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s. Aplites are usually very fine-grained, white, grey or pinkish, and their constituents are visible only with the help of a magnifying lens. Dyke

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
s and threads of aplite are commonly observed traversing granitic bosses; they occur also, though less frequently, in syenite

Syenite

Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts ....
s, diorite

Diorite

Diorite is a grey to dark grey intermediate Intrusion igneous rock composed principally of plagioclase feldspar , biotite, hornblende, and/or pyroxene....
s, quartz

Quartz

Diabase

Diabase or Dolerite is a mafic, holocrystalline, intrusion igneous rock equivalent to volcanic basalt or intrusion gabbro. In North American usage the term diabase refers to the fresh rock, whilst elsewhere the term dolerite is used for the fresh rock and diabase refers to altered material.....
s and gabbro

Gabbro

Gabbro refers to a large group of dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt. The rocks are Intrusive, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass....
s.

Aplites usually have a genetic affinity to the rocks they intersect.

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Encyclopedia

Aplite in petrology

Petrology

Intrusion

Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
in which quartz

Quartz

Feldspar

Mineral

Dike (geology)

Syenite

Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts ....
s, diorite

Diorite

Diorite is a grey to dark grey intermediate Intrusion igneous rock composed principally of plagioclase feldspar , biotite, hornblende, and/or pyroxene....
s, quartz

Quartz

Diabase

Gabbro

Granite

Granite is a common and widely occurring type of Intrusion , felsic, igneous rock rock . Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as Porphyry ....
areas, for example, are the last part of the magma

Magma

Magma is molten Rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles....
to crystallize, and correspond in composition to the quartzo-feldspathic aggregates that fill up the interspaces between the early minerals in the main body of the rock. They bear a considerable resemblance to the eutectic mixtures which are formed on the cooling of solutions of mineral salts, and remain liquid till the excess of either of the components has separated out, finally solidifying en masse when the proper proportions of the constituents and a suitable temperature are reached.

The essential components of aplites are quartz and alkali feldspar (the latter usually orthoclase

Orthoclase

Orthoclase is an important Silicate minerals mineral which forms igneous rocks. The name is from the Greek language for "straight fracture," because its two cleavage planes are at right angles to each other....
or microperthite

Perthite

Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar ....
), microcline

Microcline

Microcline is an important igneous rocks-forming Silicate minerals mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium....
and albite

Albite

Albite is a plagioclase feldspar mineral. It is the sodium Endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content....
. Crystallization

Crystallization

Crystallization is the process of formation of solid crystals Precipitation from a solution, melting or more rarely Deposition directly from a gas....
has been apparently rapid (as the rocks are so fine-grained), and the ingredients have solidified almost at the same time. Hence their crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions....
s are rather imperfect and fit closely to one another in a sort of fine mosaic of nearly equi-dimensional grains. Porphyritic feldspar

Feldspar

Granophyre

Granophyre is an igneous rock that contains quartz and alkali feldspar in characteristic angular intergrowths such as those in the accompanying image....
s and felsite

Felsite

Felsite is a very fine grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light colored rock that typically requires petrographic examination or chemical analysis for more precise definition....
s is very close, as all these rocks have nearly the same chemical composition.

The aplites associated with diorites and quartz-diabases differ in minor respects from the common aplites which accompany granites. The accessory minerals of these rocks are principally oligoclase

Oligoclase

Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite and anorthite ....
, muscovite

Muscovite

Muscovite is a Silicate minerals mineral of aluminium and potassium with formula potassiumaluminum22, or 236....
, apatite

Apatite

Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of Hydroxyl−, Fluorine−, or Chlorine− ions, respectively, in the crystal....
and zircon

Zircon

Zircon is a mineral belonging to the group of Silicate minerals. Its chemical name is zirconium silicate and its corresponding chemical formula is ZirconiumSiliconOxygen4....
. Biotite

Biotite

Biotite is a common Silicate minerals#Phyllosilicates mineral within the mica group, with the approximate chemical formula K3AlSi3O102....
and all ferromagnesian minerals

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric"....
rarely appear in them, and never in considerable amounts. Riebeckite

Riebeckite

Riebeckite is a sodium-rich member of the amphibole group of minerals, chemical formula sodium25silicon8oxygen222....
-granites have close affinities to aplites, shown especially in the prevalence of alkali feldspars. Tourmaline

Tourmaline

Tourmaline is a crystal silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classed as a semi-precious stone and the gem comes in a wide variety of colors....
also occurs in some aplites.

The rocks of this group are very frequent in all areas where masses of granite are known. They form dykes and irregular veins

Vein (geology)

In geology, a vein is a finite volume within a rock , having a distinct shape, filled with crystals of one or more minerals, which were precipitated from an fluid....
which may be only a few inches or many feet in diameter

Diameter

In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle....
. Less frequently aplite forms stocks or bosses, or occupies the edges or irregular portions of the interior of outcrop

Outcrop

Outcrop is a Geology term referring to the appearance of bedrock or superficial deposits exposed at the surface of the Earth. In most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be seen or examined closely....
s of granite. The syenite

Syenite

Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts ....
-aplites consist mainly of alkali feldspar; the diorite-aplites of plagioclase

Plagioclase

Plagioclase is a very important series of Silicate minerals minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series ....
; there are nepheline

Nepheline

Nepheline, also called nephelite , is a feldspathoid: a silica-undersaturated aluminosilicate, Sodium3PotassiumAluminium4silicon4Oxygen16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites....
-bearing aplites which intersect some elaeolite-syenites. In all cases they bear the same relation to the parent masses. By increase of quartz, aplites pass gradually, in a few localities, through highly quartzose modifications into quartz veins.