ANTIPERTHITE Meaning and
Definition
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Antiperthite is a mineralogical term referring to a symplectite texture found in certain granitic and granitic pegmatite rocks. The term is derived from the Greek word "anti," meaning "opposite," and the name "perthite," which is a type of alkali feldspar.
Antiperthite is characterized by a distinctive intergrowth of plagioclase feldspar crystals within an alkali feldspar matrix. In this texture, the plagioclase feldspar crystals are "encased" or enclosed within the alkali feldspar crystal structure, creating a reverse or inverse composition compared to the norm. The alkali feldspar typically appears as blocky or lattice-like structures, while the plagioclase feldspar forms elongated, needle-like grains nestled within.
This phenomenon occurs due to chemical exchange reactions among the feldspar crystals during solid-state metamorphism or subsolidus processes. The process begins with the diffusion of elements between the two types of feldspars, leading to the formation of alternating layers of the two minerals. Over time, internal pressure and chemical reactions result in the development of the characteristic symplectite intergrowth, distinguishing antiperthite from simpler perthitic textures.
Antiperthite can provide important insights into the geological history and metamorphic processes of the rocks in which it is found. Its study helps geologists understand the dynamic nature of rock formations and the complex chemical interactions that occur over time.
Etymology of ANTIPERTHITE
The word "antiperthite" is a combination of two terms: "anti-" and "perthite".
The prefix "anti-" comes from the Greek word "antí", meaning "against" or "opposite". In this context, it signifies that "antiperthite" is an alteration or opposite of something.
The term "perthite" refers to a type of feldspar mineral composed of two separate minerals, usually orthoclase feldspar and albite feldspar. Perthite is characterized by an exsolution texture where albite lamellae (thin layers) are embedded within the orthoclase feldspar host. The name "perthite" derives from Perth, Scotland, where it was first described in the early 19th century.
