Hornblenda

Prévia do material em texto

1
©2001 G.C. FinnBrock University
Biaxial Minerals Descriptions
• Olivine
• Pyroxenes
– Orthopyroxene
– Clinopyroxene
• Amphibole
– Hornblende
– Actinolite
• Micas
– Biotite, muscovite, chlorite
• Feldspars
– Plagioclase
– Microcline, orthoclase, sanidine
©2001 G.C. FinnBrock University
Amphiboles
• Two groups to consider:
– orthoamphiboles
– clinoamphiboles
• Similar to pyroxenes (single chain) but 
have a double chain of silica tetrahedra
elongated ŏ to c axis
• Exhibit a range of compositions with a 
corresponding range of optical 
properties. (p. 201 - compositional 
range)
• Compositions can not accurately be 
determined based on optical properties.
©2001 G.C. FinnBrock University
Classification of Amphiboles
Fe-Mg Amphiboles
– Anthophyllite (O) (Mg,Fe)7Si8O22(O H)2
– Gedrite (O) (Mg,Fe)5Al2 (Al2Si6)O22(O H)2
– Cummingtonite-grunerite (M) (Fe, Mg)7Si8O22(O H)2
Calcic Amphiboles (M)
– Tremolite-actinolite Ca2(Mg,Fe2+)5Si8O22(OH)2
– Hornblende (Na,K)0-1Ca2(Mg,Fe2+,Fe3+,Al)5(Si,Al)8O22(OH)2
– Oxyhornblende (Na,K)0-1Ca2(Mg,Fe2+,Fe3+,Al)5(Si,Al)8O22(O,OH)2
– Kaersutite NaCa2(Mg,Fe2+)4TiSi6Al2O22(OH)2
Sodic-calcic amphiboles (M)
– Katophorite Na(Na,Ca)(Mg,Fe2+,Fe3+,Al)5(Si7AlO22(OH)2
– Richertite Na(Na,Ca)(Mg,Fe2+)5Si8O22(OH)2
Sodic Amphiboles (M)
– Glaucophane Na2(Mg,Fe2+)3Al2Si8O22(OH)2
– Riebeckite Na2(Mg,Fe2+)3Fe3+2Si8O22(OH)2
– Arfedsonite-eckermanite NaNa2(Mg,Fe2+)4(Fe3+,Al)Si8O22(OH)2
Tuesday, October 23, 12
1
©2001 G.C. FinnBrock University
Biaxial Minerals Descriptions
• Olivine
• Pyroxenes
– Orthopyroxene
– Clinopyroxene
• Amphibole
– Hornblende
– Actinolite
• Micas
– Biotite, muscovite, chlorite
• Feldspars
– Plagioclase
– Microcline, orthoclase, sanidine
©2001 G.C. FinnBrock University
Amphiboles
• Two groups to consider:
– orthoamphiboles
– clinoamphiboles
• Similar to pyroxenes (single chain) but 
have a double chain of silica tetrahedra
elongated ŏ to c axis
• Exhibit a range of compositions with a 
corresponding range of optical 
properties. (p. 201 - compositional 
range)
• Compositions can not accurately be 
determined based on optical properties.
©2001 G.C. FinnBrock University
Classification of Amphiboles
Fe-Mg Amphiboles
– Anthophyllite (O) (Mg,Fe)7Si8O22(O H)2
– Gedrite (O) (Mg,Fe)5Al2 (Al2Si6)O22(O H)2
– Cummingtonite-grunerite (M) (Fe, Mg)7Si8O22(O H)2
Calcic Amphiboles (M)
– Tremolite-actinolite Ca2(Mg,Fe2+)5Si8O22(OH)2
– Hornblende (Na,K)0-1Ca2(Mg,Fe2+,Fe3+,Al)5(Si,Al)8O22(OH)2
– Oxyhornblende (Na,K)0-1Ca2(Mg,Fe2+,Fe3+,Al)5(Si,Al)8O22(O,OH)2
– Kaersutite NaCa2(Mg,Fe2+)4TiSi6Al2O22(OH)2
Sodic-calcic amphiboles (M)
– Katophorite Na(Na,Ca)(Mg,Fe2+,Fe3+,Al)5(Si7AlO22(OH)2
– Richertite Na(Na,Ca)(Mg,Fe2+)5Si8O22(OH)2
Sodic Amphiboles (M)
– Glaucophane Na2(Mg,Fe2+)3Al2Si8O22(OH)2
– Riebeckite Na2(Mg,Fe2+)3Fe3+2Si8O22(OH)2
– Arfedsonite-eckermanite NaNa2(Mg,Fe2+)4(Fe3+,Al)Si8O22(OH)2
Tuesday, October 23, 12
2
©2001 G.C. FinnBrock University
Orthoamphibole
Orthorhombic amphibole
• Anthophyllite (Mg,Fe)7Si8O22(O H)2
• Restricted to metamorphosed basaltic 
rocks
• Because it is orthorhombic it exhibits Œ
extinction in elongate sections
• All remaining amphiboles are 
monoclinic and exhibit inclined 
extinction in elongate sections
©2001 G.C. FinnBrock University
Amphibole
Monoclionic Amphiboles or Amphiboles
• most common
• all monoclinic
• generally all optically -ve
• 2 major ones to be familiar with:
– Tremolite - Actinolite
• Ca2Mg5Si8O22(OH)2 - Ca2Fe5Si8O22(OH)2
– Common Hornblende
• Ca2(Mg,Fe,Al)5Si8O22(OH)2
• Variable compositions = variable optical 
properties.
©2001 G.C. FinnBrock University
Hornblende
Refractive Index
nD = 1.60 - 1.70
nE = 1.61 - 1.71
nJ = 1.62 - 1.73
Relief, Birefringence, Retardation
• Exhibits moderate to high relief
• Birefringence 0.014-0.034
• Interference colours vary from 1st order 
orange to upper 2nd order - lower 3rd order 
colours
– Average 2nd order blue-green interference colours
Tuesday, October 23, 12
2
©2001 G.C. FinnBrock University
Orthoamphibole
Orthorhombic amphibole
• Anthophyllite (Mg,Fe)7Si8O22(O H)2
• Restricted to metamorphosed basaltic 
rocks
• Because it is orthorhombic it exhibits Œ
extinction in elongate sections
• All remaining amphiboles are 
monoclinic and exhibit inclined 
extinction in elongate sections
©2001 G.C. FinnBrock University
Amphibole
Monoclionic Amphiboles or Amphiboles
• most common
• all monoclinic
• generally all optically -ve
• 2 major ones to be familiar with:
– Tremolite - Actinolite
• Ca2Mg5Si8O22(OH)2 - Ca2Fe5Si8O22(OH)2
– Common Hornblende
• Ca2(Mg,Fe,Al)5Si8O22(OH)2
• Variable compositions = variable optical 
properties.
©2001 G.C. FinnBrock University
Hornblende
Refractive Index
nD = 1.60 - 1.70
nE = 1.61 - 1.71
nJ = 1.62 - 1.73
Relief, Birefringence, Retardation
• Exhibits moderate to high relief
• Birefringence 0.014-0.034
• Interference colours vary from 1st order 
orange to upper 2nd order - lower 3rd order 
colours
– Average 2nd order blue-green interference colours
Tuesday, October 23, 12
2
©2001 G.C. FinnBrock University
Orthoamphibole
Orthorhombic amphibole
• Anthophyllite (Mg,Fe)7Si8O22(O H)2
• Restricted to metamorphosed basaltic 
rocks
• Because it is orthorhombic it exhibits Œ
extinction in elongate sections
• All remaining amphiboles are 
monoclinic and exhibit inclined 
extinction in elongate sections
©2001 G.C. FinnBrock University
Amphibole
Monoclionic Amphiboles or Amphiboles
• most common
• all monoclinic
• generally all optically -ve
• 2 major ones to be familiar with:
– Tremolite - Actinolite
• Ca2Mg5Si8O22(OH)2 - Ca2Fe5Si8O22(OH)2
– Common Hornblende
• Ca2(Mg,Fe,Al)5Si8O22(OH)2
• Variable compositions = variable optical 
properties.
©2001 G.C. FinnBrock University
Hornblende
Refractive Index
nD = 1.60 - 1.70
nE = 1.61 - 1.71
nJ = 1.62 - 1.73
Relief, Birefringence, Retardation
• Exhibits moderate to high relief
• Birefringence 0.014-0.034
• Interference colours vary from 1st order 
orange to upper 2nd order - lower 3rd order 
colours
– Average 2nd order blue-green interference colours
Tuesday, October 23, 12
3
©2001 G.C. FinnBrock University
Hornblende
Optic Sign
• Optic sign either +ve or –ve
• 2VX angle varies from 35 to 130°, 
depending on composition
• Generally 2VX = 52 - 85° therefore 
optically -ve
©2001 G.C. FinnBrock University
Hornblende
Colour
• Hornblende is distinctly coloured and 
pleochroic in thin section. Shades of green, 
yellow-green, blue-green and brown.
Pleochroism
X Y Z
yellow-green olive green dark green
pale brown greenish dark green
greenish-brown reddish-brown red-brown
• variety of pleochroic colours.
©2001 G.C. FinnBrock University
Hornblende 
Pleochroism
© G.C. Finn, 2005
cleavage
© G.C. Finn, 2005
hbl
hbl
cpx cpx
Tuesday, October 23, 12
3
©2001 G.C. FinnBrock University
Hornblende
Optic Sign
• Optic sign either +ve or –ve
• 2VX angle varies from 35 to 130°, 
depending on composition
• Generally 2VX = 52 - 85° therefore 
optically -ve
©2001 G.C. FinnBrock University
Hornblende
Colour
• Hornblende is distinctly coloured and 
pleochroic in thin section. Shades of green, 
yellow-green, blue-green and brown.
Pleochroism
X Y Z
yellow-green olive green dark green
pale brown greenish dark green
greenish-brown reddish-brown red-brown
• variety of pleochroic colours.
©2001 G.C. FinnBrock University
Hornblende 
Pleochroism
© G.C. Finn, 2005
cleavage
© G.C. Finn, 2005
hbl
hbl
cpx cpx
Tuesday, October 23, 12
3
©2001 G.C. FinnBrock University
Hornblende
Optic Sign
• Optic sign either +ve or –ve
• 2VX angle variesfrom 35 to 130°, 
depending on composition
• Generally 2VX = 52 - 85° therefore 
optically -ve
©2001 G.C. FinnBrock University
Hornblende
Colour
• Hornblende is distinctly coloured and 
pleochroic in thin section. Shades of green, 
yellow-green, blue-green and brown.
Pleochroism
X Y Z
yellow-green olive green dark green
pale brown greenish dark green
greenish-brown reddish-brown red-brown
• variety of pleochroic colours.
©2001 G.C. FinnBrock University
Hornblende 
Pleochroism
© G.C. Finn, 2005
cleavage
© G.C. Finn, 2005
hbl
hbl
cpx cpx
Tuesday, October 23, 12
4
©2001 G.C. FinnBrock University
Hornblende
• Exhibits good amphibole cleavage on 
110 plane at 56° and 124°
• Grain shape is controlled by cleavage 
and are usually elongated Πto c axis
© G.C. Finn, 2005
Hornblende cleavages
©2001 G.C. FinnBrock University
Hornblende
Form
• Occurs as:
– slender prismatic to bladed crystals
– with a 4 or 6 sided cross section which 
exhibit amphibole cleavage at 56 and 124°
– also as anhedral irregular grains
bb
a
110
01
0
©2001 G.C. FinnBrock University
Hornblende
b
Z
Y
X
O
A
P
OA
OA
01
0
110
011
c
2VX =
52-85°
• Monoclinic
• Optic orientation:
– X^a = +3 to -19°
– Y = b
– Z^c = +12 to +39°
РOAP is Πto 010
Tuesday, October 23, 12
4
©2001 G.C. FinnBrock University
Hornblende
• Exhibits good amphibole cleavage on 
110 plane at 56° and 124°
• Grain shape is controlled by cleavage 
and are usually elongated Πto c axis
© G.C. Finn, 2005
Hornblende cleavages
©2001 G.C. FinnBrock University
Hornblende
Form
• Occurs as:
– slender prismatic to bladed crystals
– with a 4 or 6 sided cross section which 
exhibit amphibole cleavage at 56 and 124°
– also as anhedral irregular grains
bb
a
110
01
0
©2001 G.C. FinnBrock University
Hornblende
b
Z
Y
X
O
A
P
OA
OA
01
0
110
011
c
2VX =
52-85°
• Monoclinic
• Optic orientation:
– X^a = +3 to -19°
– Y = b
– Z^c = +12 to +39°
РOAP is Πto 010
Tuesday, October 23, 12
4
©2001 G.C. FinnBrock University
Hornblende
• Exhibits good amphibole cleavage on 
110 plane at 56° and 124°
• Grain shape is controlled by cleavage 
and are usually elongated Πto c axis
© G.C. Finn, 2005
Hornblende cleavages
©2001 G.C. FinnBrock University
Hornblende
Form
• Occurs as:
– slender prismatic to bladed crystals
– with a 4 or 6 sided cross section which 
exhibit amphibole cleavage at 56 and 124°
– also as anhedral irregular grains
bb
a
110
01
0
©2001 G.C. FinnBrock University
Hornblende
b
Z
Y
X
O
A
P
OA
OA
01
0
110
011
c
2VX =
52-85°
• Monoclinic
• Optic orientation:
– X^a = +3 to -19°
– Y = b
– Z^c = +12 to +39°
РOAP is Πto 010
Tuesday, October 23, 12
5
©2001 G.C. FinnBrock University
Hornblende
• Basal sections exhibit symmetrical 
extinction, slow ray Πto long diagonal 
between cleavages
• Elongated sections are length slow, and 
the Z^c extinction angle is used to 
identify hornblende
©2001 G.C. FinnBrock University
Hornblende
Basal Section
ŏ to c axis
• 4 to 6 sided grain
• and/or 2 cleavages 
at 56-124°
• Symmetrical 
Extinction
• ~ Bxo Figure
01
0
110
a
b
Yc
Z'
X'
O
A
P
©2001 G.C. FinnBrock University
© G.C. Finn, 2005
Symmetrical Extinction
© G.C. Finn, 2005
Hornblende
cleavages
EA1
EA2
EA1 = EA2
Hornblende
Tuesday, October 23, 12
5
©2001 G.C. FinnBrock University
Hornblende
• Basal sections exhibit symmetrical 
extinction, slow ray Πto long diagonal 
between cleavages
• Elongated sections are length slow, and 
the Z^c extinction angle is used to 
identify hornblende
©2001 G.C. FinnBrock University
Hornblende
Basal Section
ŏ to c axis
• 4 to 6 sided grain
• and/or 2 cleavages 
at 56-124°
• Symmetrical 
Extinction
• ~ Bxo Figure
01
0
110
a
b
Yc
Z'
X'
O
A
P
©2001 G.C. FinnBrock University
© G.C. Finn, 2005
Symmetrical Extinction
© G.C. Finn, 2005
Hornblende
cleavages
EA1
EA2
EA1 = EA2
Hornblende
Tuesday, October 23, 12
5
©2001 G.C. FinnBrock University
Hornblende
• Basal sections exhibit symmetrical 
extinction, slow ray Πto long diagonal 
between cleavages
• Elongated sections are length slow, and 
the Z^c extinction angle is used to 
identify hornblende
©2001 G.C. FinnBrock University
Hornblende
Basal Section
ŏ to c axis
• 4 to 6 sided grain
• and/or 2 cleavages 
at 56-124°
• Symmetrical 
Extinction
• ~ Bxo Figure
01
0
110
a
b
Yc
Z'
X'
O
A
P
©2001 G.C. FinnBrock University
© G.C. Finn, 2005
Symmetrical Extinction
© G.C. Finn, 2005
Hornblende
cleavages
EA1
EA2
EA1 = EA2
Hornblende
Tuesday, October 23, 12
6
©2001 G.C. FinnBrock University
Hornblende
Optic Normal Section
• one cleavage
• Inclined Extinction
• Maximum 
interference colour
• Optic Normal Figure
• Z^c = +12-34°
c
a
OA
OA
X
Z
11
0
a^c = 75°
2VX = 
52-85°
Z^c =
 +12 - +34°
Y
011
©2001 G.C. FinnBrock University
© G.C. Finn, 2005
© G.C. Finn, 2005
© G.C. Finn, 2005
Hornblende
Inclined
Extinction
Extinction
Angle
eg. Hornblende
©2001 G.C. FinnBrock University
Hornblende
Section ŏ to a axis
• Parallel Extinction
• ~ Bxa Figure
c
b
Y
01
0
Z'
O
A
P
X'
a
Tuesday, October 23, 12
6
©2001 G.C. FinnBrock University
Hornblende
Optic Normal Section
• one cleavage
• Inclined Extinction
• Maximum 
interference colour
• Optic Normal Figure
• Z^c = +12-34°
c
a
OA
OA
X
Z
11
0
a^c = 75°
2VX = 
52-85°
Z^c =
 +12 - +34°
Y
011
©2001 G.C. FinnBrock University
© G.C. Finn, 2005
© G.C. Finn, 2005
© G.C. Finn, 2005
Hornblende
Inclined
Extinction
Extinction
Angle
eg. Hornblende
©2001 G.C. FinnBrock University
Hornblende
Section ŏ to a axis
• Parallel Extinction
• ~ Bxa Figure
c
b
Y
01
0
Z'
O
A
P
X'
a
Tuesday, October 23, 12
6
©2001 G.C. FinnBrock University
Hornblende
Optic Normal Section
• one cleavage
• Inclined Extinction
• Maximum 
interference colour
• Optic Normal Figure
• Z^c = +12-34°
c
a
OA
OA
X
Z
11
0
a^c = 75°
2VX = 
52-85°
Z^c =
 +12 - +34°
Y
011
©2001 G.C. FinnBrock University
© G.C. Finn, 2005
© G.C. Finn, 2005
© G.C. Finn, 2005
Hornblende
Inclined
Extinction
Extinction
Angle
eg. Hornblende
©2001 G.C. FinnBrock University
Hornblende
Section ŏ to a axis
• Parallel Extinction
• ~ Bxa Figure
c
b
Y
01
0
Z'
O
A
P
X'
a
Tuesday, October 23, 12
7
©2001 G.C. FinnBrock University
Hornblende
Alteration
• may be altered to biotite, 
chlorite or other Fe-Mg silicates
©2001 G.C. FinnBrock University
Hornblende
Occurrence
• Hornblende is found in a variety of 
lithologies:
• Igneous (granites, through gabbros, 
syenites to ultramafics)
• metamorphic environments
• May be primary or secondary in origin
©2001 G.C. FinnBrock University
Hornblende
Distinguishing Features
• 2 cleavages
• grain shape
• inclined extinction
• pleochroism
b
Z
Y
X
O
A
P
OA
OA
01
0
110
011
c
2VX =
52-85°
Tuesday, October 23, 12
7
©2001 G.C. FinnBrock University
Hornblende
Alteration
• may be altered to biotite, 
chlorite or other Fe-Mg silicates
©2001 G.C. FinnBrock University
Hornblende
Occurrence
• Hornblende is found in a variety of 
lithologies:
• Igneous (granites, through gabbros, 
syenites to ultramafics)• metamorphic environments
• May be primary or secondary in origin
©2001 G.C. FinnBrock University
Hornblende
Distinguishing Features
• 2 cleavages
• grain shape
• inclined extinction
• pleochroism
b
Z
Y
X
O
A
P
OA
OA
01
0
110
011
c
2VX =
52-85°
Tuesday, October 23, 12
7
©2001 G.C. FinnBrock University
Hornblende
Alteration
• may be altered to biotite, 
chlorite or other Fe-Mg silicates
©2001 G.C. FinnBrock University
Hornblende
Occurrence
• Hornblende is found in a variety of 
lithologies:
• Igneous (granites, through gabbros, 
syenites to ultramafics)
• metamorphic environments
• May be primary or secondary in origin
©2001 G.C. FinnBrock University
Hornblende
Distinguishing Features
• 2 cleavages
• grain shape
• inclined extinction
• pleochroism
b
Z
Y
X
O
A
P
OA
OA
01
0
110
011
c
2VX =
52-85°
Tuesday, October 23, 12
Hornblenda
Sinal Ótico
• Sinal ótico +ve ou - ve
• Ângulo 2Vx varia de 35 a 130˚, dependendo da 
composição
• Em geral 2Vx = 52 - 85˚, portanto -ve
Tuesday, October 23, 12
Hornblenda
Cor
• Hornblenda é distintivamente colorida e pleocróica em 
seção delgada. Tons de verde, verde-amarelo, verde-
azulado e marrom
Pleocroísmo
X Y Z
verde-oliva 
amarelo
marrom claro
marrom 
esverdeado
verde
marrom 
avermelhado ou 
esverdeado
verde escuro
marrrom 
avermelhado 
escuro
• uma variadade de cores de pleocroísmo 
Tuesday, October 23, 12
Hornblenda
Pleocroísmo
Tuesday, October 23, 12
Tuesday, October 23, 12