Question

Which one of the given textural features results from exsolution?

• A. Ophitic
• B. Perthitic
• C. Graphic
• D. Glomeroporphyritic

Answer 1

The Correct Option is B

To determine which textural feature results from exsolution, we first need to understand the term exsolution. Exsolution is a process where an initially homogeneous solid solution separates into two different crystalline minerals without the addition or removal of material. This typically occurs in minerals as they cool and results in exsolved textures.

Now let's examine the options:

• Ophitic: This texture is characterized by large plagioclase crystals being enclosed by augite. It is typical of some gabbros and basalts but does not result from exsolution.
• Perthitic: This is a descriptive term for an intergrowth of two feldspars: K-feldspar and albite. This texture forms due to exsolution as K-feldspar grows and an albite phase segregates as temperature decreases. Hence, this is the texture that results from exsolution.
• Graphic: This texture appears as intergrowths that look like written characters, typically found in pegmatites, but it does not form by exsolution.
• Glomeroporphyritic: This texture features aggregates of phenocrysts in an igneous rock and is not related to exsolution.

Thus, the correct answer is Perthitic, as it specifically results from the exsolution process.

In summary, perthitic texture is a result of the exsolution process where plagioclase and potassium feldspar separate at lower temperatures, leading to the characteristic intergrowth.