Minerals: an archive of physical and optical properties

1. Minerals
(an archive)
Prepared by:
Muhammad Talha
4th prof. (Minpet)
Institute of Geology, PU, Lahore.
Presented to:
Dr. Saif Ur Rehman
talha.geo@outlook.com

2. 2
Olivine (Nesosilicate)
Forsterite, Fayalite
Pyroxene (Inosilicate)
Enstatite, Ferrosilite, Augite, Diopside,
Hedenbergite, Pigeonite, Omphacite,
Amphibole (Inosilicate)
Tremolite, Actinolite, Hornblende, Grunerite,
Cummingtonite, Anthophyllite, Glaucophane
Mica (Phyllosilicate)
Muscovite, Biotite, Phlogopite, Glauconite
Feldspar (Tectosilicate)
Anorthite, Bytownite, Labradorite, Andesine,
Oligoclase, Albite, Anorthoclase, Sanidine,
Orthoclase, Microcline
Carbonate
Calcite, Dolomite, Azurite, Malachite, Siderite
Sulfide
Pyrite, Chalcopyrite, Chalcocite,
Bornite
Oxide
Hematite, Magnetite, Ilmenite, Cuprite
Hydroxide
Limonite, Geothite
Misc.
Quartz (Tectosilicate)
Fluorite (Halide)
Apatite (Phosphate)
Turquoise (Hydrated Phosphate)
Chrysocolla (Hydrated phyllosilicate)
Dioptase (Hydrated cyclosilicate)
Garnet Group (Nesosilicate)
Tourmaline Group (Cyclosilicate)

3. 3
Olivine (Nesosilicate)
• Forsterite
• Fayalite

4. Forsterite (Nesosilicate; Olivine)
4
Formula: Mg2SiO4
Colour: Green, pale yellow, colourless, white
Birefringence: (0.03-0.04) Grey, yellow, blue,
pink
Relief: high
Cleavage plane: Perfect {010}, imperfect {100}
Angle of cleavage:
Extinction angle:
Twinning: On {100}, {011} & {012}
Pleochroism: Weak

5. Fayalite (Nesosilicate: Olivine)
5
Formula: Fe2SiO4
Colour: Greenish pale yellow, brown
Birefringence: (0.04-0.05) Blackish grey, yellow, blue, white,
green
Relief: very high
Cleavage plane: {010} moderate, {100} imperfect
Angle of cleavage:
Extinction angle:
Twinning: On [100]; also on [031], as trillings
Pleochroism: Faint; Pale, yellow, orange, reddish brown

6. 6
Pyroxene (Inosilicate)
Opx
• Enstatite
• Ferrosilite
Cpx
• Augite
• Diopside
• Hedenbergite
• Pigeonite
• Omphacite

7. Enstatite (Inosilicate; Opx)
7
Formula: Mg2SiO6
Colour: Olive green, yellow, brown, white
Birefringence: (0.01-0.02) Blackish grey
Relief: Moderate
Cleavage plane: Good {210}
Angle of cleavage:
Extinction angle:
Twinning: Lamellar {100}
Pleochroism: Weak; pale green to pale orange

8. Ferrosilite (Inosilicate; Opx)
8
Formula: FeSiO3
Colour: Dark brown, black
Birefringence: (0.01-0.02) Pinkish brown, greenish
white
Relief: high
Cleavage plane: Good {210}
Angle of cleavage:
Extinction angle: Parallel
Twinning:
Pleochroism: Weak; pinkish brown (x), greenish brown
(z)

9. Augite (Inosilicate; Cpx)
9
Formula: (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6
Colour: Purplish brown, greenish brown, black
Birefringence: 0.032
Relief: high
Cleavage plane: Good {110}
Angle of cleavage: 87° between {110} and {110}
Extinction angle: z : c = 35°-48°
Twinning: Simple or multiple on {100}, also on {001}
Pleochroism: visible
X= pale green, pale brown, green, greenish yellow
Y= pale brown, pale yellow-green, violet
Z= pale green, grayish green, violet

10. Diopside (Inosilicate; Cpx)
10
Formula: CaMgSi2O6
Colour: light to dark green, brown, colorless, white, grey, pale
violet
Birefringence: 0.03
Relief: high
Cleavage plane: Good on {110}
Angle of cleavage: 87º and 93º
Extinction angle:
Twinning: Simple & multiple twins common on {100} & {001}
Pleochroism: N/A

11. Hedenbergite (Inosilicate; Cpx)
11
Formula: CaFeSi2O6
Colour: Brownish green, black
Birefringence: 0.029
Relief: high
Cleavage plane: {110}
Angle of cleavage:
Extinction angle:
Twinning: Simple {100}, {010}
Pleochroism: Weak; (pale green, bluish
green)

12. Pigeonite (Inosilicate; Cpx)
12
Formula: (Ca,Mg,Fe)(Mg,Fe)Si2O6
Colour: Brown, greenish brown-black
Birefringence: (0.021 - 0.030)
Relief: high
Cleavage plane: Good on {110}, (110) ^ (110) ~87°
Angle of cleavage:
Extinction angle:
Twinning: Commonly twinned simply or multiply on {100} or
{001}
Pleochroism: Weak to moderate;
X = colorless, pale green, brown
Y = pale brown, pale brownish green, brownish pink
Z = colorless, pale green, pale yellow Pigeonite exolution lamellae in Augite

13. Omphacite (Inosilicate; Cpx)
13
Formula: (Ca,Na)(Mg,Fe2+,Al)Si2O6
Colour: Green to dark green; colorless to pale green in thin
section
Birefringence: 0.023
Relief: high
Cleavage plane: Good on {110}, {110} ^ {110} ≈87°; parting on
{100}
Angle of cleavage:
Extinction angle: 36-44°
Twinning: Single and polysynthetic twinning common on {100}
Pleochroism: Weak;
X = colorless
Y = very pale green
Z = very pale green, blue-green

14. 14
Amphibole (Inosilicate)
• Tremolite
• Actinolite
• Hornblende
• Grunerite
• Cummingtonite
• Anthophyllite
• Glaucophane

15. Tremolite (Inosilicate; Amphibole)
15
Formula: Ca2(Mg5.0-4.5Fe2+
0.0-0.5)Si8O22(OH)2
Colour: White, gray, lavender to pink, light green, light yellow
Birefringence: 0.026
Relief: Moderate
Cleavage plane: Perfect on {110}, partings on {010} and {100}
Angle of cleavage: 56° and 124°
Extinction angle: 15-20°
Twinning: Simple or multiple, common parallel to {100}; rarely parallel to {001}
Pleochroism: Absent

16. Actinolite (Inosilicate; Amphibole)
16
Formula: Ca2(Mg4.5-2.5Fe2+
0.5-2.5)Si8O22(OH)2
Colour: pale to dark green, yellowish green and black. White or grey when in asbestos
Birefringence: 0.023
Relief: Moderate
Cleavage plane: perfect along {110}
Angle of cleavage: cleavage angle in two directions are at ≈56° and 124 in cross section, and in one direction for longitudinal
section
Extinction angle: 10-15°
Twinning: simple or lamellar
Pleochroism: weak; yellow to green

17. Hornblende (Inosilicate; Amphibole)
17
Formula: Ca2(Mg, Fe, Al)5 (Al, Si)8O22(OH)2
Colour: Black to dark green or brown
Birefringence: 0.014 – 0.018
Relief: High
Cleavage plane:
Angle of cleavage: Two directions intersecting at 124 and 56
degrees
Extinction angle: Symmetrical to cleavages
Twinning:
Pleochroism: Strong; yellow -green to dark brown

18. Grunerite (Inosilicate; Amphibole)
18
Formula: Fe7Si8O22(OH)2
Colour: Ashen, brown, brownish green, dark gray
Birefringence: 0.033 - 0.043
Relief: High
Cleavage plane: Perfect prismatic {110}
Angle of cleavage: two good, 55o
Extinction angle: 10° to 15°
Twinning: simple, lamellar, very common
Pleochroism: Mg-rich none, Fe-rich colourless or
pale

19. Cummingtonite (Inosilicate; Amphibole)
19
Formula: (Mg,Fe2+)2(Mg,Fe2+)5Si8O22(OH)2
Colour: Dark green, brown, gray, beige; colorless to pale green in thin section
Birefringence: (0.025 − 0.037) Birefringence decreases systematically with Mg
content
Relief: Moderate
Cleavage plane: Good on {110}
Angle of cleavage: intersecting at 54 and 126°
Extinction angle: Inclined
Twinning: Simple and lamellar – common
Pleochroism: Weak; found primarily in samples with higher Fe content
X = Y = colorless; Z = pale green

20. Anthophyllite (Inosilicates; Amphibole)
20
Formula: Mg2Mg5Si8O22(OH)2
Colour: Gray to green, brown, and beige
Birefringence: Low-moderate (0.017 - 0.023)
Relief: Moderate
Cleavage plane: Perfect on {210}, imperfect on {010}, {100}
Angle of cleavage: N/A
Extinction angle: Straight, Parallel
Twinning: N/A
Pleochroism: Weak – colorless to pale yellow

21. Glaucophane (Inosilicates; Amphibole)
21
Formula: Na2(Mg3Al2)Si8O22(OH)2
Colour: Gray, navy blue, lavender-blue
Birefringence: 0.021
Relief: Moderate
Cleavage plane: Good on [110] and on
[001]
Angle of cleavage: intersects at 56 and
124°
Extinction angle: Parallel extinction in
XPL
Twinning: N/A
Pleochroism: Strong/Distinct
pleochroism;

22. 22
Mica (Phyllosilicate)
• Muscovite
• Biotite
• Phlogopite
• Glauconite

23. Muscovite (Phyllosilicate; Mica)
23
Formula: KAl3Si3O10(OH)2
Colour: Colorless, silvery-white, beige, grey
Birefringence: 0.035 – 0.042
Relief: Moderate
Cleavage plane: Perfect on {001}
Angle of cleavage:
Extinction angle: Parallel to cleavage in all orientations (bird's eye
maple).
The maximum extinction angle is less than 3 degrees
Twinning: Common on the [310], less common on the {001}
Pleochroism: Weak

24. Biotite (Phyllosilicate; Mica)
24
Formula: K(Mg,Fe)3(AlSi3O10)(F,OH)2
Colour: Dark brown, greenish-brown, blackish-brown, yellow, white
Birefringence: High
Relief: Moderate
Cleavage plane: Perfect on {001}
Angle of cleavage:
Extinction angle: Parallel to cleavage in all orientations (bird's eye
maple).
The maximum extinction angle is less than 3 degrees
Twinning: Common on the [310], less common on the {001}
Pleochroism: Moderate to strong;
brown-orange-yellow-green

25. Phlogopite (Phyllosilicate; Mica)
25
Formula: KMg3(AlSi3O10)(F,OH)2
Colour: Brownish red, dark brown, yellowish brown, green, white
Birefringence: 0.028 - 0.045
Relief: Moderate
Cleavage plane: {001} Perfect
Angle of cleavage:
Extinction angle: Parallel to cleavage in all orientations (bird's eye
maple).
The maximum extinction angle is less than 3 degrees
Twinning: Composition plane {001}, twin axis [310]
Pleochroism: Visible;
X= yellow
Y=Z= brownish red, green, yellow

26. Glauconite (Phyllosilicate; Mica)
26
Formula: (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2
Colour: Blue-green, green-yellow
Birefringence: 0.020 - 0.032
Relief: Moderate
Cleavage plane: Perfect [001]
Angle of cleavage:
Extinction angle:
Twinning:
Pleochroism: X = yellow-green, green
Y = Z = deeper yellow, bluish green
PPL
XPL

27. 27
Feldspar (Tectosilicate)
Plagioclase
• Anorthite
• Bytownite
• Labradorite
• Andesine
• Oligoclase
• Albite
Alkali Feldspar
• Anorthoclase
• Sanidine
• Orthoclase
• Microcline

28. Anorthite (Tectosilicate; Feldspars; Plagioclase)
28
Formula: Ca(Al2Si2O8)
Colour: Colourless, reddish grey, white
Birefringence: 0.012–0.013
Relief: Moderate
Cleavage plane: Perfect [001] good [010] poor [110]
Angle of cleavage: Intersect at about 93-94o angles.
Extinction angle: Inclined
Twinning: Polysynthetic twinning
Pleochroism: N/A

29. Bytownite (Tectosilicate; Feldspars; Plagioclase)
29
Formula: (Ca,Na)[Al(Al,Si)Si2O8]
Colour: Colorless, white, grey
Birefringence: 0.010 - 0.011
Relief: Low
Cleavage plane: Perfect on [001], good on [010]
Angle of cleavage:
Extinction angle:
Twinning: Polysynthetic and pericline twinning
Pleochroism: N/A

30. Labradorite (Tectosilicate; Feldspars; Plagioclase)
30
Formula: (Ca,Na)[Al(Al,Si)Si2O8]
Colour: Pale green, blue, colourless, grey-white
Birefringence: 0.008 - 0.010
Relief: Low
Cleavage plane: Perfect on {001}, less perfect on {010}, distinct on {110}
Angle of cleavage: intersecting at near 90°
Extinction angle:
Twinning: Common by Albite, Pericline, Carlsbad, Baveno, or Manebach twin laws
Pleochroism: N/A

31. Andesine (Tectosilicate; Feldspars; Plagioclase)
31
Formula: (Na,Ca)[Al(Si,Al)Si2O8]
Colour: White, gray, green, yellow, flesh-red
Birefringence: 0.009
Relief: Low
Cleavage plane: Perfect on {001}, good on {010}
Angle of cleavage: 86○
Extinction angle:
Twinning: Common following albite & pericline twin laws
Pleochroism: N/A

32. Oligoclase (Tectosilicate; Feldspars; Plagioclase)
32
Formula: (Na,Ca)[Al(Si,Al)Si2O8]
Colour: Colourless, white, pale yellow
Birefringence: 1st order
Relief: low
Cleavage plane: {001} perfect, {010} good, {110} poor
Angle of cleavage:
Extinction angle:
Twinning: polysynthetic
Pleochroism: N/A

33. Albite (Tectosilicate; Feldspars; Plagioclase)
33
Formula: Na(AlSi3O8)
Colour: White to grey, bluish, greenish, reddish
Birefringence: δ = 0.010
Relief: Low
Cleavage plane: Perfect on {001}, very good on {010}, imperfect on {110}
Angle of cleavage: The cleavage angle is about 90º
Extinction angle:
Twinning: Common giving polysynthetic striae on {001} or {010}also contact, simple and
multiple
Pleochroism: N/A

34. Anorthoclase (Tectosilicate; Alkali-Feldspar)
34
Formula: (Na,K)AlSi3O8
Colour: white, colourless, greyish pink
Birefringence: δ = 0.008
Relief: Low
Cleavage plane: Perfect on [001], other partings
Angle of cleavage: The cleavage angle is about 90º
Extinction angle: 1-5○
Twinning: Polysynthetic twinning, produces a grid pattern on
[100]
Pleochroism: N/A

35. Sanidine (Tectosilicate; Alkali Feldspar)
35
Formula: K(AlSi3O8)
Colour: Colourless, white, grey, yellowish white, or reddish
white
Birefringence: δ = 0.007
Relief: Low
Cleavage plane: {001} perfect, {010} good
Angle of cleavage:
Extinction angle:
Twinning: Carlsbad – common
Baveno, Manebach - rarer
Pleochroism: N/A

36. Orthoclase (Tectosilicate; Alkali Feldspar)
36
Formula: KAlSi3O8
Colour: Colorless to white, Greenish white, Grayish yellow, Pale pink
Birefringence: 0.004
Relief: Low
Cleavage plane: Perfect on {001}, good on {010}
Angle of cleavage: Cleavages intersect at 90°. It can be difficult to
see
cleavage in thin section due to orthoclase's low relief.
Extinction angle: X^a = 6°-14°, Y^c = -13° to 21°, Z = b
Twinning: Common as Carlsbad, Baveno and Manebach
Pleochroism: N/A

37. Microcline (Tectosilicate; Alkali Feldspar)
37
Formula: K(AlSi3O8)
Colour: White, grey, greyish yellow, yellowish, tan, salmon-pink, bluish green
Birefringence: Up to first order white (roughly 0.007)
Relief: Low
Cleavage plane: Perfect on [001], good on [010]
Angle of cleavage: Cleavages intersect at 90°41'
Extinction angle: Inclined extinction to cleavage
Twinning: Carlsbad, Baveno, Manebach, polysynthetic on albite and pericline
laws.
Typically displays albite twinning and pericline twinning This combination
leads to a grid pattern, hence microcline displays gridiron twinning.
Pleochroism: N/A

38. 38
Carbonate
• Calcite
• Dolomite
• Azurite
• Malachite
• Siderite

39. Calcite (Carbonate)
39
Formula: CaCO3
Colour: White, Yellow, Red, Orange, Blue, Green, Brown, Gray etc.
Birefringence: 0.154 - 0.174 (Due to extreme birefringence,
interference colors are high order pastel pink, green and
creamy white)
Relief: Low to moderate (Calcite is characterized by change in relief
during a 360°rotation of the stage; the crystals is said to
“twinkle” during rotation)
Cleavage plane: 1,3 – rhombohedral. Perfect on {1011}
Angle of cleavage: three direction with 60○ and 120○
Extinction angle: symmetrical to cleavage traces
Twinning: Common by four twin laws
Pleochroism: N/A
XPL
PPL

40. Dolomite (Carbonate)
40
Formula: CaMg(CO3)2
Colour: Colourless, white, gray, reddish-white, brownish-
white, or pink
Birefringence: 0.179
Relief: Moderate
Cleavage plane: Perfect on {1011}
Angle of cleavage: 3 directions of cleavage not at right
angles.
Extinction angle: Parallel
Twinning: Common as simple contact twins
Pleochroism: N/A

41. Azurite (Carbonate)
41
Formula: Cu3(CO3)2(OH)2
Colour: Azure blue, blue, light blue, or dark blue
Birefringence: 0.108
Relief: High
Cleavage plane: Perfect on {011}, fair on {100}, poor on
{110}
Angle of cleavage:
Extinction angle:
Twinning: Rare, twin planes {101}, {102} or {001}
Pleochroism: Visible shades of blue;
with absorption Z greater than Y greater than X.

42. Malachite (Carbonate)
42
Formula: Cu2(CO3)(OH)2
Colour: Bright green, with crystals deeper shades of
green,
even very dark to nearly black
Birefringence: 0.254
Relief: Very High
Cleavage plane: Perfect on {201}, fair on {010}
Angle of cleavage:
Extinction angle:
Twinning: Common as contact or penetration twins on
{100}
and {201}. Polysynthetic twinning also present
Pleochroism: Visible;
X ^ c 23½° = nearly colourless
XPL
PPL
PPL

43. Siderite (Carbonate)
43
Formula: FeCO3
Colour: Pale yellow to tannish, grey, brown, green, red,
black
and sometimes nearly colorless
Birefringence: 0.242
Relief: High
Cleavage plane: Perfect on {1011}
Angle of cleavage:
Extinction angle:
Twinning: Lamellar uncommon on{0112}
Pleochroism: N/A
Quartz grains, metamorphic rock fragments and siderite ooids (alteration product
of glauconite diagenesis) surrounded by pore-filling berthierine

44. 44
Sulfide
• Pyrite
• Chalcopyrite
• Chalcocite
• Bornite
Cu-Fe Sulfide Minerals

45. Pyrite (Sulfide)
45
Formula: FeS2
Colour: Pale brass-yellow
Birefringence: N/A [Opaque]
Relief: N/A
Cleavage plane: Indistinct on {001}; partings on {011} and
{111}
Angle of cleavage:
Extinction angle: N/A
Twinning: Penetration and contact twinning
Pleochroism: N/A

46. Chalcopyrite (Sulfide)
46
Formula: CuFeS2
Colour: Brass yellow, often with an iridescent tarnish
Birefringence: N/A [Opaque]
Relief: N/A
Cleavage plane: Indistinct on {011}
Angle of cleavage:
Extinction angle: N/A
Twinning: Twinned on {112} and {012}, penetration or
cyclic
Pleochroism: N/A
(Peacock ore;
iridescent chalcopyrite)

47. Chalcocite (Sulfide)
47
Formula: Cu2S
Colour: Blue black, gray, black, black gray, or steel gray
Birefringence: N/A [Opaque]
Relief: N/A
Cleavage plane: Indistinct on (110)
Angle of cleavage:
Extinction angle: N/A
Twinning: Common on {110} yielding pseudohexagonal stellate
forms
Pleochroism: N/A

48. Bornite (Sulfide)
48
Formula: Cu5FeS4
Colour: Copper-red to pinchbeck-brown, quickly
tarnishing to an iridescent purplish surface.
Birefringence: N/A [Opaque]
Relief: N/A
Cleavage plane: Poor on {111}
Angle of cleavage:
Extinction angle: N/A
Twinning: Penetration twins on [111]
Pleochroism: N/A
“Peacock ore”

49. 49
Oxide
• Hematite
• Magnetite
• Ilmenite
• Cuprite
Hydroxide
• Limonite
• Geothite

50. Hematite (Oxide)
50
Formula: Fe2O3
Colour: Steel-grey to black in crystals and massively
crystalline
ores, dull to bright "rust-red" in earthy, compact, fine
grained material
Birefringence: δ = 0.280
Relief: Very High
Cleavage plane: None;
may show partings on {0001} and {1011}
Angle of cleavage:
Extinction angle:
Twinning: Penetration and lamellar
Pleochroism: Weak;
O = brownish red
E = yellowish red

51. Magnetite (Oxide; Spinel Group)
51
Formula: Fe2+Fe3+
2O4
Colour: Greyish black or iron black
Birefringence: [Isotropic]
Relief: Very High
Cleavage plane: Indistinct, good parting on {Ill}
Angle of cleavage:
Extinction angle: N/A
Twinning: On {111} as both twin and composition plane,
the
spinel law, as contact twins
Pleochroism: N/A

52. Ilmenite / Manaccanite (Oxide)
52
Formula: FeTiO3 [Opaque]
Colour: Iron-black; gray with a brownish tint in reflected light
Birefringence: Strong; O = pinkish brown, E = dark brown
(bireflectance)
Relief:
Cleavage plane: N/A
Angle of cleavage:
Extinction angle:
Twinning: {0001} simple, {1011} lamellar
Pleochroism: Weak
Ilmenite crystals in a Gabbro

53. Cuprite (Oxide)
53
Formula: Cu2O
Colour: Dark red to cochineal red, sometimes almost
black
Birefringence: N/A [Opaque]
Relief: Very High
Cleavage plane: Imperfect/Fair
Interrupted on {111}, more rarely on {001}
Angle of cleavage:
Extinction angle:
Twinning: Penetration twins
Pleochroism: Visible

54. Limonite (Hydroxide Mineraloid; Amorphous)
54
Formula: (Fe,O,OH,H2O)
Colour: Various shades of brown and yellow
Birefringence: N/A [Opaque]
Cleavage plane: Absent

55. Geothite (Hydroxide)
55
Formula: α-Fe3+O(OH)
Colour: brownish black, yellow-brown, reddish
brown
Birefringence: 0.133 - 0.134 [Opaque]
Relief: Very High
Cleavage plane: Perfect {010}
Angle of cleavage:
Extinction angle:
Twinning:
Pleochroism: Visible;
X = red b/yellow b = clear yellow
Y = red a/yellow c = brown-yellow
Z = red c/yellow a = orange-yellow

56. 56
Misc.
• Quartz (Tectosilicate)
• Fluorite (Halide)
• Apatite (Phosphate)
• Turquoise (Hydrated Phosphate)
• Chrysocolla (Hydrated phyllosilicate)
• Dioptase (Hydrated cyclosilicate)
• Garnet Group (Nesosilicate)
• Tourmaline Group (Cyclosilicate)

57. Quartz (Tectosilicate)
57
Formula: SiO2
Colour: Various, commonly colourless or white
Birefringence: +0.009 (B-G interval)
Relief: Low
Cleavage plane: {0110} Indistinct
Angle of cleavage:
Extinction angle: zero, undulose extinction also common
Twinning: Dauphiné law, Brazil law, Japan law, Others for beta-
quartz...
Pleochroism: N/A

58. Fluorite (Halide)
58
Formula: CaF2
Colour: Purple, lilac, golden-yellow, green, colourless, blue, pink,
champagne, brown
Birefringence: isotropic
Relief: Moderate
Cleavage plane: Octahedral, perfect on {111}, parting on {011}
Angle of cleavage:
Extinction angle:
Twinning: On {111}, usually as interpenetrating cubes
(e.g.,Strzegom,
Poland), but also as contact spinel twins (e.g. Naica,
Mexico and Chumar Bakhoor, Pakistan)
Pleochroism: Colourless to violet
XPL
PPL
(isotropic)
(violet)

59. Apaptite (Phosphate)
59
Formula: Ca5(PO4)3(F,Cl,OH)
Colour: Colorless, white, yellow, brown, gray, red, pink, purple, blue,
green
Birefringence: 0.002–0.008
Relief: high
Cleavage plane: [0001] indistinct, [1010] indistinct
Angle of cleavage:
Extinction angle:
Twinning: Rare contact twins on {1121}. Twin plane {1013} rare. Also
twinning reported on {1010} and {1123}
Pleochroism: Visible; weak to strong in colour crystals
Apatite inclusions in Amphibole

60. Turquoise (Hydrated Phosphate)
60
Formula: CuAl6(PO4)4(OH)8 · 4H2O
Colour: bright blue, sky-blue, pale green, blue-green,
turquoise
blue, apple-green, green-gray
Birefringence: 0.040
Relief: Moderate
Cleavage plane: Perfect on {001}, good on {010}, usually
N/A
Angle of cleavage:
Extinction angle:
Twinning:
Pleochroism: Weak;
X= colorless
Z= pale blue or pale green

61. Chrysocolla (Hydrated Phyllosilicate)
61
Formula: Cu2-xAlx(H2-xSi2O5)(OH)4 · nH2O
Colour: Green, bluish green, blue, blackish blue to black, or
brown and rarely yellow
Birefringence: 0.023 - 0.050
Relief: Moderate
Cleavage plane: N/A
Angle of cleavage:
Extinction angle:
Twinning: N/A
Pleochroism: absent

62. Dioptase (Hydrated Cyclosilicate)
62
Formula: CuSiO3 · H2O
Colour: Dark teal, emerald green
Birefringence: 0.052
Relief: High
Cleavage plane: Perfect in three
directions
Angle of cleavage:
Extinction angle:
Twinning: On {1011}, uncommon
Pleochroism: Weak

63. Garnet Group (Nesosilicate)
63
Formula:X3Z2(SiO4)3
X = Mg, Ca, Fe(II), Mn(II), etc.
Z = Al, Fe(III), Cr(III), V(III) etc.
Trace amounts of Sn may replace Fe(III)
Colour: virtually all colors, blue is very rare
Birefringence: N/A [Isotropic]
Relief: High
Cleavage plane: Indistinct
Twinning: N/A
Pleochroism: N/A
Major Minerals/Varieties: Pyrope
Mg3Al2Si3O12
Almandine Fe3Al2Si3O12
Spessartine Mn3Al2Si3O12
Andradite Ca3Fe2Si3O12
Grossular Ca3Al2Si3O12
Uvarovite Ca3Cr2Si3O12

64. Garnet Group (Nesosilicate)
64
Garnets with internal foliation

65. Tourmaline Group (Cyclosilicate)
65
Formula: (Ca,K,Na)(Al,Fe,Li,Mg,Mn)3(Al,Cr, Fe,V)6(BO3)3(Si,Al,B)6O18(OH,F)4
Colour: black, brown, green, red, pink, blue, and gray. White, colorless, yellow, orange, and purple colors are less common. Crystals are
frequently multicolored, containing two or more distinct colors
Birefringence: 0.018 to 0.040;
typically about 0.020 but in dark stones it may reach 0.040
Relief: Medium
Cleavage plane: Indistinct; {110} and {101} very poor
Angle of cleavage:
Extinction angle: Longitudial sections show parallel extinction and are length fast
Twinning: rare at {1010} or {1011}
Pleochroism: Moderate to strong;
Red Tourmaline: Definite; dark red, light red
Green Tourmaline: Strong; dark green, yellow-green
Brown Tourmaline: Definite; dark brown, light brown
Blue Tourmaline: Strong; dark blue, light blue

66. Tourmaline Group (Cyclosilicate)
66
Major varieties/mineral:
Achroite: Colorless variety of Elbaite Tourmaline.
Buergerite: Rare mineral of the Tourmaline group, occurring almost exclusively at Mexquitic, San Luis Potosí, Mexico.
Dravite: It is usually brown in color, and the term may be corrupted to include all forms of brown Tourmaline.
Elbaite: Elbaite is the most transparent and colorful form of Tourmaline. The term Elbaite may be corrupted in the gemstone industry to refer specifically to green
Tourmaline.
Indicolite: Blue variety of Elbaite Tourmaline.
Liddicoatite: Uncommon member mineral of the Tourmaline group found primarily in Madagascar. It is the calcium analogue of Elbaite, containing calcium in
its chemicalformula instead of sodium.
Rubellite: Pink to red variety of Elbaite Tourmaline.
Schorl: Individual member mineral of the Tourmaline group. It is black in color, and the term may be corrupted to include any very dark Tourmaline forms.
Uvite: Uncommon member mineral of the Tourmaline group, usually found in metamorphic environments such as marbles.
Watermelon Tourmaline: Variety of Elbaite Tourmaline that is green on the outside and red on the inside

67. Tourmaline Group (Cyclosilicate)
67

68. Tourmaline Group (Cyclosilicate)
68
Torumaline crystal (basal section)
Tourmaline crystals in peraluminous Granite
Green tourmaline aggregates in Luxullianite

69. 69
References
 alexstrekeisen.it
 mindat.org
 minerals.net
 wikipedia.org
 mineralminers.com
 webmineral.com
 ScienceDirect
 pinterest.com
 Atlas of Igneous Rocks and Their Textures, by W. S. MacKenzie (Author), C. H. Donaldson (Author), C. Guilford
 Igneous minerals in thin section; Kurt Hollocher Geology Department, Union College Schenectady, NY U.S.A.
 Smith College - Geology 222b – Petrology
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