1) How to distinguish between plagioclase and microclain? 2) Explain the composi
ID: 231916 • Letter: 1
Question
1) How to distinguish between plagioclase and microclain?2) Explain the composition variation of K-Feldspar and albite exsolution lamellae in perthite ?
3) What is the different between binary and eutectic phase diagrams ? Draw them ?
4) Explain how mineral forms ?
5) What is Zoning and how zoning is formed in the Plagioclase Explain ? 1) How to distinguish between plagioclase and microclain?
2) Explain the composition variation of K-Feldspar and albite exsolution lamellae in perthite ?
3) What is the different between binary and eutectic phase diagrams ? Draw them ?
4) Explain how mineral forms ?
5) What is Zoning and how zoning is formed in the Plagioclase Explain ? 1) How to distinguish between plagioclase and microclain?
2) Explain the composition variation of K-Feldspar and albite exsolution lamellae in perthite ?
3) What is the different between binary and eutectic phase diagrams ? Draw them ?
4) Explain how mineral forms ?
5) What is Zoning and how zoning is formed in the Plagioclase Explain ?
Explanation / Answer
1) In thin section plagioclase feldspar shows lamellar twinning and microcline shows cross hatched twinning.
2) 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). Typically the host grain is orthoclase or microcline, and the lamellae are albite.
3)
4) Minerals form primarily from cooling of lava or magma into crystals to form different minerals depending upon the chemical composition of the magma. Secondary minerals can form from evaporation and precipitation from watery solutions like calcite.
5) When a mineral crystallizes from a melt it forms a tiny crystal at first. then this crystal reacts with the residual melt to form another layer of the mineral of a slightly different chemical composition over the earlier crystal. this process continues till there is no melt left. this variation in mineral composition from core to rim is called zoning.
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