Aplite

Aplite a group name for light mineral-rich, fine-grained and dense leukokrate dyke rocks associated with plutonic or metasomatic altered rocks. Aplites are characterized by a very low content of at Mafiten (below 5 percent).

Etymology and terminology

The name derives from the Greek Aplite πλος ( haplos ), which simply means. It was developed by A. J. Retz introduced in 1800 for the first time and later ( 1823) by Karl Caesar von Leonhard in the scientific literature, probably in reference to the relatively simple mineralogical structure of the rock.

The prefix Aplo - is used to denote brighter, mineralogically simple composite rocks which are depleted of ferromagnetic minerals Saxon. Examples are the Aplodiorit and Aplogranit. In 1935 introduced in his special petrography of the igneous rocks of Walter Ehrenreich Tröger term Aplosyenit is now no longer used.

Dissemination

Due to their association with granitoids and occasionally more basic igneous rocks such as Gabbro aplites occur worldwide ( basement, orogens, Batholithe, intrusions and magmatic provinces ).

Training

Aplites are very bright, dense, fine -grained to aphanitische gear or wire rocks. Their color can be pink from white to light gray to vary or flesh-colored. The gears can be zoned. Your structure is usually very even grained and nichtporphyrisch. The grain size range in the submillimeter range for detecting the mineral is therefore a magnifying glass is required. Due to the low and very uniform grain sizes may be assumed in magmatic incurred aplites of a very rapid and contemporaneous crystallization. The crystal forms are predominantly hypidiomorph, the structure is like a mosaic. The transition strength of the aplites moves mostly in the centimeter range, rare in the decimeter, and occasionally in the meter range. Very rarely, they may form smaller sticks or irregular accumulations inside or in peripheral areas of plutons. At pegmatites often find aplitische edge zones.

Chemical composition

Aplites are predominantly of quartz, alkali feldspar (usually orthoclase or Mikroperthit ) composed and plagioclase. They are very mafic minerals to depleted (usually biotite ), with their color number is usually less than 5 ( hololeukokrat ), in conjunction with more basic intrusives but this can increase to 10. Your chemistry often is very similar to the composition of the fine-grained porphyritic gusset filling of parent rocks. Strikingly, there is this to the eutectic composition of granitoids. My alkali feldspar may occasionally also accept porphyry trends, quartz, however, almost never. This underlines their socialization with Granophyren, quartz porphyries and Felsiten. With diorites and associated aplites Quarzdioriten usually show a slightly modified composition, they lead predominantly plagioclase ( oligoclase ) and muscovite, apatite and zircon. Syenitaplite show mainly alkali feldspar, why can join in the rare Eläolith nepheline syenites also ( nepheline leading aplites were formerly known as Aploide ). The quartz content is growing sharply, aplites can go by very rich in quartz modifications such Beresit in quartz veins.

Biotite and other forensic ferromagnetic (Fe -Mg- containing) minerals, or rarely as good as come not before.

Besides pneumatolytic minerals such as topaz and fluorite also tourmalines can sometimes occur.

Aplite often show increased concentrations of the elements beryllium and lithium.

Formation

Aplites can be caused by two very different processes:

• Magmatic
• Metasomatic

Magmatic origin

In fulfillment of the puzzle criterion, that is, the seamless joining of the host rock and the seamless transition closure of the columns can be assumed that aplites represent the molten filling of aufreißenden elongation column or columns systems in plutonic rock bodies. Your injection is given as residual eutectic melt in the magmatic state in the late stage of the respective plutons. The small grain size of the aplites suggests a rapid cooling of the residual melt.

Metasomatic origin

If the evaluation of the puzzle criterion is negative, a metasomatic origin of aplites must be assumed that their formation occurred in situ by chemical reactions ( metasomatic differentiation) in the solid state shifts of the host rock did not materialize. The chemical mass transfer is usually effective only in the centimeter to decimeter. The host rock ( Paläosom ) impoverished usually in bright ingredients such as feldspars ( it is thereby a melanosome ), which then in Leukosom, the aplite, are concentrated. Metasomatic aplites are usually enriched in SiO2 compared with their parent rock.

Varieties

Aplogranite or Granitaplite are light-colored rocks with the same composition as granite, but in which biotite is rare or absent. In addition to the Granitapliten there are syenite, diorite and Gabbroaplite.

Mikroaplite are extremely fine -grained fillings of cavities and cracks in syntectonic granitoids. With progressive deformation the granitoids can not fully crystallize because of becoming effective tensile stresses. In addition, already crystallized grains are split or torn. The remaining residual melt is therefore forced to a rapid crystallization process in the resulting cavities. The resulting fillings consist of tiny plagioclase ( albite, oligoclase ) and quartz grains with edges Xenomorphs often lobed and toothed. Mikroaplitische fillings cause no significantly deeper tempered, micro- cracked Kline.

Natural stone places

Due to its occurrence as a relatively thin mighty dykes Aplite trade infrequently, because they occur only in limited quantities.

Example:

• Grigio Argento: aplite from Sardinia