Does plagioclase have exsolution?
Does plagioclase have exsolution?
Plagioclase feldspars exhibit exsolution microtextures in three compositional ranges, the Peristerite, Bøggild and Huttenlocher ‘miscibility gaps’ shown in orange on Fig. 4 and in white in Fig. 8. These intergrowths are coherent and usually below the resolution of an optical microscope.
What is exsolution in geology?
exsolution, in mineralogy, process through which an initially homogeneous solid solution separates into at least two different crystalline minerals without the addition or removal of any materials.
What is plagioclase in geology?
Plagioclase is a member of the feldspar group (like orthoclase) and is a framework silicate. Plagioclase consists of a solid solution between the albite and anorthite end-members, and together with quartz is the most common of the rock forming minerals.
What is exsolution lamellae in geology?
Exsolution is a process by which a solid solution phase unmixes into two separate phases in the solid state. These lamellae result from the exsolution of a separate pyroxene phase from a host grain due to subsolidus re-equilibration (that occurs while the mineral is in the solid state) during slow cooling.
What kinds of textures are indicative of the exsolution process?
Exsolution texture, a general term for the texture of mineral intergrowth formed by solid exsolution, is a common texture in minerals from both magmatic and metamorphic rocks. This texture is important for understanding variations of metamorphic conditions.
What are perthite and Antiperthite?
A perthite is an intimate intergrowth of sodic and potassic feldspar resulting from subsolidus exsolution (unmixing of two minerals). An antiperthite is an intergrowth arising due to exsolution where potassic feldspar is present as blebs or lamellae within a sodic feldspar.
Which feldspar has exsolution lamellae?
Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi3O8, in composition).
What is gas exsolution?
This causes a reduction in pore pressure that lowers the gas solubility and results in exsolution. The exsolved gas then displaces water from storage, and the specific storage increases because gas compressibility is typically much greater than that of water or aquifer material.
What is the composition of plagioclase?
| Physical Properties of Plagioclase | |
|---|---|
| Chemical Classification | Silicate |
| Specific Gravity | 2.6 to 2.8 |
| Diagnostic Properties | Perfect cleavage, with cleavage faces intersecting at right angles and striations often present on cleavage faces. Well-defined crystals are extremely rare. |
| Chemical Composition | NaAlSi3O8 – CaAl2Si2O8 |
What causes exsolution lamellae?
Exsolution lamellae are fine crystals that were dissolved entirely in their host mineral structures at high temperature (e.g., clino- and orthopyroxenes) and/or pressure (e.g., majorite-pyroxenes), but are produced when their host minerals lose the solubility as a result of cooling to low temperatures (T-controlled …
How Myrmekite is formed?
myrmekite, irregular, wormy penetration by quartz in plagioclase feldspar; these wartlike, wormlike, or fingerlike bodies may develop during the late stages of crystallization of igneous rocks if the two minerals (quartz and feldspar) grow simultaneously in the presence of a volatile phase.
What is the geologic occurrence of plagioclase?
Geologic Occurrence of Plagioclase. Members of the plagioclase group are the most common rock-forming minerals. They are important to dominant minerals in most igneous rocks of the Earth’s crust. They are major constituents in a wide range of intrusive and extrusive igneous rocks including granite, diorite, gabbro, rhyolite, andesite,…
What is plagioclase used for in construction?
Construction, Decorative and Architectural Stone. Plagioclase minerals are important constituents of some building stone and crushed stone such as granite and trap rock. These rocks are also cut and polished for use as countertops, stair treads, wall panels, building facing, monuments, and many other types of decorative and architectural stone.
What is the difference between Na-plagioclase and CA-plagoclase?
Na-plagioclase belongs to acid plagioclase, and Ca-plagioclases belong to basic plagioclase ( Table 3.3 ). In fact pure albite contains 68.7% SiO 2, and a pure anortite comprises only 43.2% SiO 2. Plagioclase is usually found in the form of granular aggregates in kaolinite, while well-formed crystals are rare.
What are the physical properties of plagioclase feldspar?
Physical Properties of Plagioclase Minerals All feldspar minerals have two directions of perfect cleavage. It is usually easy to distinguish plagioclase feldspars because their two planes of cleavage intersect at 90-degree angles, and their cleavage faces often display striations.
