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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Vaibhav Singh posted an Question
August 27, 2021 • 12:30 pm
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30 points
30 points
- IIT JAM
- Geology (GG)
270. asterism is a property displayed by which group of minerals? a alumino silicates b. olivine c. mica d. feldspar (bhu-2014)
270. Asterism is a property displayed by which group of minerals? A Alumino silicates B. Olivine C. Mica D. Feldspar (BHU-2014) I have read that asterism (scattering effect similar to chatoyancy) is possible in some crystals particularly of hexagonal systems.{reference-C.Klein}.. Here Mica is always monoclinic,,,In aluminosilicates Kyanite -triclinic , sillimanite ,Andalusite-- orthorhombic,,,, in Feldspars , plagioclase-triclinic,alkali feldspars-monoclinic,triclinic ,,,,,Olivine---Orthorhombic. then No answer should be correct na??
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Saurabh 1 Best Answer
It has to be Mica. No, it's just a speculation or a misleading fact that only hexagonal minerals shows asterism. Generally they are found to be containing some inclusions or fibres that causes some reflection or transmission of the light incident on the surface. Strictly speaking, You can go through some research papers as well where they have clearly mentioned that even Diopside and Phlogopite(a type of mica obviously) , shows asterism pertaining to the rutile inclusions or refractive index contrast . Cornelis Klein stated this fact but it's not always true, actually sometimes even the complete statements are omitted which ultimately leads to irrelevant conclusions. I would suggest you to go through some classic research papers on the gemology and optical phenomenon related to gemstones.