Microscopic Mineralogy- the study of minerals under microscope

MICROSCOPY LAB
SUBMISSION
-By
Devaki Nandana V V
18GG20036.

Determinative
Mineralogy
Laboratory

OPTICAL PROPERTIES OF MINERALS
I. UNDER PLANE
POLARISED LIGHT
● Colour
● Relief
● Pleochroism: Pleochroic/Non-Pleochroic
● Pleochroic Scheme:
● Uniaxial Mineral: E= Colour P; O = Colour Q
● Biaxial Mineral: X= Colour P; Y = Colour Q; Z =
Colour R
● Habit:
Equant/Ovoid/Elongated/Prismatic/Tabular/Acicula
r/Flaky etc
● Shape: Euhedral/Subhedral/Anhedral
● Cleavage/Fracture
● E(i) Cleavage angle for minerals with more than 1
set of cleavage:

OPTICAL PROPERTIES OF MINERALS
II. UNDER CROSSED NICOLS ● Isotropic/Anisotropic
● Nature of Extinction in anisotropic
minerals: Straight/Inclined
(i) Extinction Angle:
● Interference Colour and its Order:
● Twinning
● Optic Sign: Uniaxial (+ve/-Ve)/Biaxial
(+ve/-ve)

Minerals to be studied:-
30 Quartz (I/M) Chloritoid(M) Apatite(I)
Microcline(I) Orthopyroxene(I/M) Sphene(I/M)
Orthoclase(I/M) Clinopyroxene(I) Rutile(M)
Plagioclase(I/M) Olivine(I/M) Cordierite(M)
Tourmaline Staurolite(M) Epidote(M/I)
Biotite(M/I) Garnet(M) Zircon(I/M)
Chlorite(M) Green Spinel(M) Scapolite(M)
Muscovite(M/I) Tremolite/Actinolite(M) Calcite(M/I)
Kyanite(M) Hornblende(M) Monazite(M)
Sillimanite(M) Glaucophane Nepheline(I)

Sialic Minerals Accessory Minerals
Feldspars Apatite
Nepheline Monazite
Quartz Zircon
Rare Accessory Minerals
Femic Minerals Calcite
Amphiboles Cordierite
Biotite Garnet
Olivine Muscovite
Pyroxene Rutile
Scapolite
Alteration products Sphene
Chlorite Tourmaline

Quartz
Under Plane Polarised Light:
● Colour: Colourless
● Shape and Outline: Anhedral
● Relief and RI: Low relief
● Birefringence: Low birefringence
● Pleochroism: Non-pleochroic
● Cleavage and Fracture: Absence of
cleavage
Under Crossed Nicols:
● Anisotropic or Isotropic: Anisotropic
● Interference Colour: 1° Yellow
● Twinning: No Twinning
● Uniaxial/Biaxial: Uniaxial
● Optic Sign: +ve

Microcline
Under Plane Polarised Light
● Habit: Irregular, equant
● Shape and Outline: Anhedral to subhedral
● Relief and RI: Low relief (<Qtz)
● Cleavage and Fracture: Present
● Interference Colour: 1° Grey
● Twinning: Cross-Hatched / Tartan Twinning
● Uniaxial/Biaxial: Biaxial
● Optic Sign: -ve
● Nature of extinction: Inclined
Image Description:
● Image showing CROSS HATCHED
TWINNING in microcline

Orthoclase
● Habit: Elongated tabular grains
● Crystal system: Monoclinic
● Shape and Outline: Anhedral to subhedral
● Relief and RI: Low relief (<Qtz)
● Twinning: Carlsbad Twinning
● Optic Sign: -ve
● Nature of extinction: Inclined or parallel
extinction
Image Description:
● Image showing Zoned crystal of orthoclase
under XPL

Plagioclase
● Shape and Outline: Lath shaped
● Relief and RI: Low relief
● Cleavage and Fracture: Cleavage present
● Anisotropic or Isotropic: Isotropic
● Twinning: Lamellar Twinning
● Optic Sign: -ve/+ve
Image Description:
● In the ﬁgure, plagioclase is identiﬁed by
low relief and lamellar twinning.

Tourmaline
● Colour: Green to Dark Green to Brown
● Habit: Acicular
● Shape and Outline: Prismatic crystals with
striations
● Relief and RI: Moderately high relief
● Pleochroism: Strongly dichroic
● E-Light green/light pink
● O-Dark Green
● Cleavage and Fracture: Transverse fracture
present, no cleavage.
● Nature of extinction: Straight extinction
● Interference Colour: 2° Interference colour
● Twinning: Absent
● Optic Sign: -ve
Image Description
● Figure showing tourmaline with 2°
Interference colour

Biotite
● Colour: Yellow to Dark Brown
● Habit: Flaky habit
● Shape: Tabular to prismatic
● Crystal system: Monoclinic
● Relief and RI: Moderate relief
● Pleochroism: Strongly pleochroic
● Cleavage and Fracture: 1 set of Basal cleavage
● Interference Colour: High order interference
colour
● Twinning: None, Twin axis[310]
● Optic Sign: -ve
Image Description:
● Image showing Zircon inclusions in Biotite
sample

ChloriteUnder Plane Polarised Light:
● Colour: Pale Green to Green
● Habit: Tabular
● Shape and Outline: Found as scales or plates
similar to micas
● Pleochroism: Strongly pleochroic
● Cleavage and Fracture: 1 set of perfect
cleavage
● Nature of extinction: Straight Extinction
● Interference Colour: 1° Interference colour
(Ink Blue)
● Twinning: Multiple twinning on {001} is
common
Image Description:
● Upper image showing Chlorite sample under
PPL showing pale green colour while lower
one is under CN showing Ink blue colour

Muscovite
● Habit: Flaky habit
● Relief and RI: Moderate Relief
● Shades of yellow and brown
● Cleavage and Fracture: 1 set perfect basal
cleavage
● Interference Colour: 3°- 4° interference
colour
● Twinning: Twin-plane {110} may be present
● Optic Sign: -ve
Image Description:
● The higher birefringence of muscovite
distinguishes it from other micas
● Figure showing muscovite in schists

Kyanite
● Habit: Bladed habit
● Shape and Outline: Elongated
● Relief and RI: Very high relief
● Cleavage and Fracture: 1 set cleavage
● Nature of extinction: Inclined extinction
● Interference Colour: 1° interference
colour
● Twinning: Twinning is frequent
● Optic Sign: -ve

Sillimanite
● Habit: Acicular
● Shape and Outline: Elongated
● Cleavage and Fracture: 1 set Basal
cleavage
colour
● Optic Sign: +ve

Chloritoid
● Colour: Lavender Blue - Pale Blue - Pale
Yellow
● Habit: Tabular
● Shape and Outline: Euhedral
● Relief and RI: High relief
● Pleochroism: Strongly pleochroic (From a
dark inky-blue to yellow)
● Cleavage and Fracture: 1 set of perfect
Cleavage
(Magnetic)
● Nature of extinction: Low extinction angle
colour
● Twinning: Present
● Optic Sign: +ve/-ve

Orthopyroxene
A) ENSTATITE
● Habit: Euhedral
● Shape and Outline: Equant
● Cleavage and Fracture: Cleavage in two
directions intersecting nearly at right
angles
colour
● Twinning: A simple twinning along {100}
● Optic Sign: +ve

Orthopyroxene
B) FERROSILITE
● Colour: Pale Green (z); Yellow (y); Pale Pink
(x)
● Habit: Massive
● Shape and Outline: Equant
● Pleochroism: Pleochroic
● Cleavage and Fracture: 2 sets of cleavage
colour
● Twinning: Twinning on {100}
● Optic Sign: -ve

Clinopyroxene
A) Diopside(mg-rich)
● Colour: Colourless (Di rich)
● Habit: Equant
● Pleochroism: Absent
● Cleavage and Fracture: 2 sets of Cleavage
(Z^C~=40°)
● Interference Colour: 2° interference colour
● Optic Sign: +ve
Special feature:
● Distinguished from Orthopyroxene by the
higher birefringence

Clinopyroxene
B) Hedenbergite(Fe-rich)
● Colour: Pale to Dark Green
● Habit: Equant
● Pleochroism: Absent
● Cleavage and Fracture: 2 sets of Cleavage
(Z^C~=40°)
● Interference Colour: 2° interference colour
● Optic Sign: +ve
Special feature:
● Distinguished from Orthopyroxene by the
higher birefringence

Olivine
● Habit: Equant
● Shape and Outline: Oval
● Cleavage and Fracture: Cleavage absent;
● Fractures present
● Interference Colour: High 2° interference
colour

Staurolite
● Colour: Dark Brown, Reddish-brown,
Yellow-brown;
● pale golden yellow in thin section.
● Habit: Euhedral Prismatic
● Shape and Outline:
● Relief and RI: High relief
● Pleochroism: Yellow to colourless
● Cleavage and Fracture: 1 set of cleavage
● Subconchoidal fracture
● Twinning: Rarely observed in thin sections
● Optic Sign: +ve

Garnet
● Colour: Pale pink-colourless
● Habit: Rounded grains, massive granular
● Shape and Outline: Euhedral to subhedral
● Relief and RI: High relief (1.714-1.887)
● Pleochroism: None
● Cleavage and Fracture: No distinct Cleavage
● Interference Colour: The garnets are
isometric, and pyrope and almandine are
truly isotropic. Spessartine, grossular and
andradite may show weak anisotropism.
● Optic Sign: -ve
1.Under PPL 2.UCN

Green Spinel
● Colour: Colorless, pale gray
● Habit: Octahedrons
● Shape and Outline: Anhedral
● Relief and RI: High
● Cleavage and Fracture: Absent
● Interference Colour: Invariably isotropic
● Twinning: Common
● Uniaxial/Biaxial: Isotropic
● Optic Sign: -ve
1.Under CN 2.Under PPL

Tremolite/
Actinolite
● Colour: Colorless
● Habit: Columnar, bladed, or acicular crystals
elongate parallel to the c axis
● Shape and Outline: Fibrous
● Relief and RI: Moderate positive
● Pleochroism: Absent or very weak
● Cleavage and Fracture: Good in two
directions
● Interference Colour: Order II green
● Twinning: Simple and lamellar twins on
{100}
● Optic Sign: -ve
1.Under PPL 2.UCN

Hornblende
● Colour: Green or Brown
● Habit: Elongated Habit
● Shape and Outline: Tabular
● Relief and RI: Moderate
● 1.61-1.76
● Birefringence=0.15
● Pleochroism: Strongly Pleochroic
● Cleavage and Fracture: 2 Sets of Cleavage
● Interference Colour: 2°-3° interference
colour, masked by the body colour
● Twinning: Simple and lamellar twinning
1.Hornblende showing pleochroism
2.Basal section of hornblende, showing the two
cleavages intersecting at 120°/60°

Glaucophane
● Colour: Blue
● Habit: Acicular to Columnar Crystals.
● Relief and RI: Moderate
● Birefringence= δ = 0.021
● Pleochroism: From blue to violet
● Interference Colour: Higher-order
interference colour
● Twinning: Polysynthetic twinning with
{01-12} as twin-plane
● Optic Sign: -ve
Image Description:
● Glaucophane showing pleochroism
Sytrongly Pleochroic.
X-Colourless/Yellow
Y-Lavender-blue
Z-Blue(Prismatic)

Apatite(Ca5
(PO4
)3
(OH, F, Cl))
Under Plane Polarised Light :
● Colour: Colourless/ White
● Habit: Crystal habits
● Shape and Outline: Short and tabular
● Relief and RI: Low to moderate relief
(>Qtz, <Pyr)
● Pleochroism: Weak to moderate pleochroism
(>Qtz, <Pyr)
● Birefringence: low(0.004)
● Cleavage and Fracture: Indistinct
Under Crossed Nicols :
● Twinning: Rare
● Optic Sign: -ve
● Nature of extinction: Shows straight
extinction
Image Description:
● Image showing Perfectly euhedral basal
section of apatite under PPL

Sphene
● Colour: Colourless, brown
● Habit: Euhedral to subhedral
● Relief and RI: Very High positive
● Pleochroism: Absent to weak
● Cleavage and Fracture: Sphene often has
prominent parting (parallel to 221)
● Interference Colour: High-order cream,
pearl-gray; or anomalous blue/brown
● Twinning: Simple twinning on {100} is
common
● Optic Sign: +ve
1.Under PPL 2.UCN

Rutile
● Colour: Blood red, brownish
● Habit: Elongate tetragonal prism with square
or octagonal cross-sections
● Shape and Outline: Rounded grains
● Relief and RI: High – Very High positive
● Pleochroism: Absent – weak
● Cleavage and Fracture: Barely visible in thin
sections; after {110} and {100}
● Interference Colour:High-order cream
(often is masked by colour)
● Twinning: Rare; in large crystals
● Optic Sign: +ve
1.Under PPL 2.UCN

Cordierite
● Habit: Anhedral grains or irregular
porphyroblastic grains
● Relief and RI: Low Relief
● Pleochroism: Non Pleochroic
● Cleavage and Fracture: Fair cleavage on
{010}; but it may not show in sections.
● Interference Colour: 1 order Int Colour
● Twinning: Parquet Twinning
1.Under PPL 2.UCN

Epidote
● Colour: Colorless, pale yellow, pale green,
greenish yellow, yellowish green
● Habit: Often found as anhedral grains or
granular aggregates
● Shape and Outline:Crystals are columnar,
prismatic, bladed,
● Relief and RI: High positive
● Pleochroism: Colourless to yellow and
green.
● Cleavage and Fracture: Perfect basal cleavage
{001}.
● Interference Colour: Order II – III (very
bright or ‘ﬂuorescent’); increasing with
increase in iron content.
● Twinning: Multiple normal twinning on
{100} is moderately common.
● Optic Sign: -ve
1.Under PPL 2.UCN

Zircon
● Colour: Colorless (usually), to pale brown,
pale yellow, or gray.
● Habit:Euhedral to subhedral
● Shape and Outline:Elongated
● Relief and RI: Very high relief positive
● Pleochroism: Absent to weak
● Cleavage and Fracture: Absent
● Interference Colour: Order III-IV; bright
detrital grains commonly show high-grade
white
● Optic Sign: +ve

Scapolite
● Habit: Prismatic
● Shape and Outline: Slender Prisms
● Relief and RI: Low
● Pleochroism: Non Pleochroic
● Cleavage and Fracture: 2 Sets of Cleavage
● Anisotropic or Isotropic: Almost
isotropic with compressibilities
● Interference Colour: 2-3 order Int colour
● Optic Sign: -ve
1.Under PPL 2.UCN

Calcite
● Colour: Colorless
● Habit: Anhedral
● Relief and RI: Relief variable
● Low(1.486->E-ray) to moderately high
(1.658->O-ray) RI
● Birefringence=0.172
● Interference Colour: High-order
● Twinning: Polysynthetic twinning with
{01-12} as twin-plane
● Optic Sign: -ve

Monazite
● Colour:
● Habit: Blocky euhedral crystals
● Relief and RI: High
● Pleochroism:
● Cleavage and Fracture:
● Anisotropic or Isotropic:
● Interference Colour: Strong interference
colors from upper third to fourth orders
● Twinning:
● Uniaxial/Biaxial:
● Optic Sign:
1.Under PPL 2.UCN

Nepheline
● Colour: Colorless (often cloudy)
● Habit: Subhedral to euhedral crystals
● Relief and RI: Low negative
● Pleochroism:
● Cleavage and Fracture: Poor basal on {0001}
and prismatic {10-10}; usually not seen in
thin section
● Interference Colour: Order I gray to white;
basal sections are dark.
● Twinning: Rare
● Optic Sign: -ve

Microscopic Mineralogy- the study of minerals under microscope

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Microscopic Mineralogy- the study of minerals under microscope