What minerals have exsolution lamellae?
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What minerals have exsolution lamellae?
They include ilmenite rods and magnetite lamellae in olivine; K-feldspar, Mg-Al-Cr titanomagnetite and/or ilmenite, quartz, and garnet rods in clinopyroxene; pyroxene and rutile lamellae in garnet; and lamellae of monazite and an unknown phase in apatite.
What are 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 …
What is mineral exsolution?
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. In most cases, it occurs upon cooling below the temperature of mutual solubility or stability of the solution.
What is Perthitic exsolution?
A perthite is an intimate intergrowth of sodic and potassic feldspar resulting from subsolidus exsolution (unmixing of two minerals). Accordingly, plutonic rocks exhibit intra – crystalline textures in alkali feldspar crystals that are not seen in volcanic rocks.
What is another name for potassium feldspar?
Synonyms for potassium feldspar include: Potash Feldspar. Alkali Feldspar. K-spar.
What causes exsolution?
Exsolution occurs only in minerals whose compositions vary between two or more pure endmember compositions. 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 causes Exsolution?
What is the most common potassium feldspar?
microcline
In some igneous rocks and in most metamorphic rocks, microcline is the common potassium feldspar. Microcline can accommodate only a little sodium and, like orthoclase, may occur with albite. All the potassium feldspars can contain more sodium at high temperatures than at low. Alkali feldspars occur in many rocks.
The exsolution lamellae are crystallographically controlled by the host minerals. They occur as one or more groups of oriented rods/needles strictly aligned along the structural defects of the host minerals. Exsolution texture induced by cooling: Clinopyroxene (Cpx) exsolution in orthopyroxene (Opx) or vice versa.
When does exsolution occur in a metastable mineral?
Exsolution occurs only in minerals with two or more pure endmember compositions that cannot mix together in normal conditions, or in metastable minerals with complicated solid solutions through ion substitutions at high temperature or pressure. Exsolution texture displays the host mineral and the intergrowth of lamellae.
Where is exsolutionlamellae pyroxene found in a peridotite?
Pyroxene with exsolution lamellae in a peridotite from Monte Duria (Adula nappe, Central Alps, Northern Italy). XPL image. 10x (Field of view = 2mm) Pyroxene with exsolution lamellae in a peridotite from Monte Duria (Adula nappe, Central Alps, Northern Italy).
Why are feldspar crystals so complex in structure?
Feldspars are structurally complex minerals. The complexity arises from the fact that Na, Ca, and K plus Si and Al do not easily replace each other in the lattice because of different ionic radii and charges. Exsolution is common because feldspar crystals that are stable at high temperature tend to break down when cooling.