302-pp21 - Quiz 8 results 1 Wulfenite(79 2 Purpurite(79 3...

Quiz 8 results
1:
1:
Wulfenite (79%
Wulfenite (79%
)
)
2:
2:
Purpurite
Purpurite
(79%
(79%
)
)
3.
3.
Varascite
Varascite
(79%
(79%
)
)
4:
4:
Wolframite
Wolframite
(74%
(74%
)
)
5:
5:
Barite (53%
Barite (53%
)
)
6:
6:
Celestine (68%
Celestine (68%
)
)
Bonus:
Bonus:
Gibsite
Gibsite
(32%
(32%
)
)
Average: 82.6%
Highest grade: 108%
A: 7
B: 5
C: 3
D: 2
F: 2

GY 302: Crystallography &
Mineralogy
GY 302: Crystallography &
Mineralogy
UNIVERSITY OF SOUTH ALABAMA
Lecture 21: Inosilicates 1
Pyroxenes and Pyroxenoids
Lecture 21: Inosilicates 1
Pyroxenes and Pyroxenoids

Class VIII Minerals
1.
Sorosilicates
2.
Cyclosilicates
(3, 4 and 6 fold coordination)
Last Time

Sorosilicates
Mineral Formula System
Zoisite Ca
2
Al
3
O(SiO
4
)(Si
2
O
7
)(OH) Orthorhombic
Clinozoisite Ca
2
Al
3
O(SiO
4
)(Si
2
O
7
)(OH) Monoclinic
Epidote Ca
2
(Al,Fe)Al
2
O(SiO
4
)(Si
2
O
7
)(OH) Monoclinic
Allanite (Ca,Ce)
2
(Fe,Fe)Al
2
O(SiO
4
)(Si
2
O
7
)(OH) Monoclinic
Lawsonite CaAl
2
SiO
7
(OH)
2
·H
2
O Orthorhombic
Pumpellyite Ca
2
MgAl
2
(SiO
4
)(Si
2
O
7
)(OH)2·H
2
O Monoclinic
Vesuvianite (Idocrase) Ca
10
Mg
2
Al
4
(SiO
4
)
5
(Si
2
O
7
)
2
(OH)
4
Tetragonal
Hemimorphite Zn
4
Si
2
O
7
(OH)
2
·(H
2
O) Orthorhombic

Hemimorphite
[Zn
4
Si
2
O
7
(OH)
2
·H
2
O]
Crystal:
Orthorhombic
Pt. Group:
2mm
Habit:
massive to mammillary
SG:
3.45;
H:
5
L:
vitreous;
Str:
white
Col: colorless, brown, to grey
Clev:
perfect [001]
Optics:
Biaxial (+); bir=0.020
n
α
=1.61; n
β
=1.62, n
γ
=1.736
Sorosilicate Minerals
http://webmineral.com/data/Hemimorphite.shtml
Named after the hemimorphic nature of the crystals.

Cyclosilicates
Mineral Formula System
Beryl Be
3
Al
2
Si
6
O
18
Hexagonal
“Tourmaline” (Na,Ca)(Li,Mg,Al)(Al,Fe,Mn)
6
(BO
3
)
3
(Si
6
O
18
)(OH)
4
Hexagonal (Trigonal)
Cordierite Al
3
(Mg, Fe)
2
(AlSi
5
O
18
) Orthorhombic
Axinite (Ca, Mn, Fe)
3
Al
2
(BO
3
)Si
4
O
12
(OH) Triclinic
Dioptase CuSiO
2
(OH)
2
Hexagonal (Trigonal)
Silicate rings come in 3, 4 and 6 fold
structures. 8-fold structures also
occur in nature (e.g., sulfur)

Cyclosilicate Minerals
6 fold ring structure

Beryl
[Be
3
Al
2
Si
6
O
18
]
Crystal:
Hexagonal
Pt. Group:
6/m 2/m 2/m
Habit:
euhedral, columnar
SG:
2.76;
H:
7.5-8
L:
vitreous;
Str:
white
Col:
blue, yellow, red, green
Clev:
imperfect
Optics:
Uniaxial (-); bir=0.004-0.007
n
e
=1.564; n
w
=1.568
Cyclosilicate Minerals
(6-fold rings)
http://webmineral.com/specimens/picshow.php?id=123
From the ancient Greek, beryllos, signifying a "precious blue-green color of sea water" stone.