For the first part please answer the above the questions for the following sets of minerals under thin section.
Set 1
Garnet
It is nonopaque
Color: Colorless to pinkish
Apparent relief: Very high +
Crystal shape: Rounded or equant
Crystal habit: If well-formed it could have 6 or 8 sides in thin section
Cleavage:
Alteration produced: May have trails or sections rich in inclusions of quartz, biotite
Under XPL
It is isotrophic
Range of interference: Nil
No twinning
Set2
Quartz, Plagioclase, K-feldspar
They are nonopaqueHave no pleochroism. Are colorless in thin section.
Crystal shape: Triclinic
Crystal habit: Anhedral or euhedral grains
Apparent relief:
Alpha = 1.527-1.577
Beta = 1.531-1.585
Gamma = 1.534-1.590
Cleavage: (110) is extremely poor cleavage, (010) quite good cleavage, and (001) is an impeccable cleavage. Cleavages intersect at approximately 93-94 degrees.
Alteration produced: No alteration is produced.
Under XPL
It is anisotrophic
Range of interference colors: 0.007-0.013
Maximum birefringence colors under thin section are normally white or first-order grey.
Maximum extinction angle inclined
No twinning.
Set3
Olivine, Orthopyroxene, Clinopyroxene, Biotite, Hornblende
It is opaque.
It is pleochroic. Normally colorless, gray, pale brown or pale green, darker colors linked to iron-rich varieties. Pale pink to green pleochroism.
Crystal shape: Orthorhombic
Crystal habit: Irregular, stubby prismatic, and massive. Longitudinal areas typically rectangular.
Apparent relief:
High-positivenalpha=1.664-1.745nbeta=1.672-1.753ngamma = 1.694-1.771
Cleavage: Archetypal pyroxene cleavages parallel to {110} that intersect at right angle.
Alteration produced: In most cases, it changes to a fg, light colored amphibole (uralite) or may alter to chlorite, serpentine, biotite, carbonates as well or other silicates.
Under XPL
It is anisotrophic.
Range of interference colors
Lower to mid second order interference.
Maximum birefringence of 0.018-0.034
Maximum extinction angle of 480
It is twinned, simple in addition to lamellar twins and composition planes that may blend to create a herringbone pattern.
After answering the questions, please summarize the characteristics features for identification of each of the above minerals under a petrographic microscope. (Garnet, Olivine, Orthopyroxene, Clinopyroxene, Amphibole, Biotite, Plagioclase, K-spar, Quartz)
Garnet
High relief in thin section. In thin section, the color is a pale form of the hand sample color; in addition, it is normally more lightly colored compared to spinel.
Olivine
Rounded or equant crystals with curving cracks in addition to colorless serpentine. Lacks color and cleavage and has a distinctive birefringence.
Orthopyroxene
First-order colors, low birefringence. Thin wavy and irregular lamellae. Parallel extinction in longitudinal zones, pale pink-green pleochroism.
ClinopyroxeneInclined extinction, second-order interference colors, higher birefringence, optimally positive than opx, and low 2V.
Amphibole
Has intense inky blue colors entirely distinctive. Normally have poikilitic plates instead of euhedral xls.
Biotite
Perfect mica cleavage in many areas. Palest when cleavage E-W. Basal areas have low birefringence, no cleavage, as well as little or no pleochroism.
Plagioclase
Cleavage and hardness (6-6.5). Lacks twinning and pleochroism. Chemical zoning is apparent; the calcic center has a bigger extinction compared to the sodic rim.
K-spar
Normally portrays good cleavage and possesses a dusty appearance from minute alteration inclusions. The inclusions comprises of sericite and muscovite, and indicate high interference colors.
Quartz
Have irregular grains, unaltered and clear. Could also indicate strained extinction.
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