General Information
|
| Chemical
Formula: |
KAlSi3O8 |
| Composition: |
Molecular Weight = 278.33 gm |
| |
Potassium 14.05 % K 16.92 % K2O |
| |
Aluminium 9.69 % Al 18.32 % Al2O3 |
| |
Silicon 30.27 % Si 64.76 % SiO2 |
| |
Oxygen 45.99 % O |
| |
______ ______ |
| |
100.00 % 100.00 % = TOTAL OxIDE |
| Empirical
Formula: |
KAlSi3O8 |
| Environment: |
Intrusive and
extrusive igneous,
and metamorphic rocks. |
| IMA
Status: |
Approved IMA 1960 |
| Locality: |
Common world wide
occurrences. Madagascar |
| Name
Origin: |
From the Greek orthos -
"right" and kalo -" I cleave" in allusion to the
mineral's right angle of good cleavage. |
| Synonym: |
Adularia |
| |
Orthose |
| |
Orthoclase Images
|
| Prismatic
bi-terminated crystal of orthoclase |
|
Click on the picture to go to Orthoclase crystal.
|
| |
©
Image by A. Darbellay |
Crystallography
|
| Axial
Ratios: |
a:b:c =0.6636:1:0.5534 |
| Cell
Dimensions: |
a = 8.625, b = 12.996, c = 7.193, Z
= 4; beta = 116.016ø V = 724.57 Den(Calc)= 2.55 |
| Crystal
System: |
Monoclinic-Prismatic H-M Symbol
(2/m) Space Group: C2/m |
| x
Ray Diffraction: |
By Intensity(I/Io):
3.18(1)4.02(0.9) 3.8(0.8) |
|
|
Physical Properties
|
| Cleavage: |
[001] Perfect, [010] Good |
| Color: |
colorless, greenish, grayish
yellow, white, or pink. |
| Density: |
2.56 |
| Diaphaniety: |
Transparent to translucent |
| Fracture: |
Uneven - Flat surfaces (not
cleavage) fractured in an uneven pattern. |
| Habits: |
Prismatic - Crystals Shaped like
Slender Prisms (e.g. tourmaline)., Massive - Granular - Common texture
observed in granite and other igneous rock., Blocky - Crystal shape
tends to be equant (e.g. feldspars). |
| Hardness: |
6 - Orthoclase |
| Luminescence: |
None. |
| Luster: |
Vitreous (Glassy) |
| Streak: |
white |
| |
Optical Properties
|
| Optical
Data: |
Biaxial (-), a=1.518, b=1.522,
g=1.523-1.524, bire=0.0050-0.0060, 2V(Calc)=52-70, 2V(Meas)=65-75.
Dispersion relatively strong. |
| Pleochroism
(x): |
colorless. |
| Pleochroism
(y): |
colorless. |
| Pleochroism
(z): |
colorless. |
| |
Classification
|
| Dana
Class: |
Tectosilicate
Al-Si Framework |
| |
with
Al-Si frameworks |
| |
(Na,Ba) feldspars |
| |
- Orthoclase
KAlSi3O8 C2/m 2/m
|
| |
- Sanidine
(K,Na)(Si,Al)4O8 C2/m 2/m
|
| |
- Hyalophane
(K,Ba)Al(Si,Al)3O8 C2/m 2/m
|
| |
Celsian BaAl2Si2O8 I21/c 2/m |
| |
- Microcline KAlSi3O8 C1- -1
|
| |
- Anorthoclase (Na,K)AlSi3O8
C1- -1
|
| |
- Rubicline ! (Rb,K)AlSi3O8 P1-
-1
|
| Strunz Class: |
Silicates |
| |
ectosilicates (network) without anions
unfamiliar to the tetraheders |
| |
STRUNZ - Silicates [Tectosilicates (network)
without anions unfamiliar to the tetraheders {Feldspar group,
Buddingtonite - Orthocl |
| |
- Buddingtonite (NH4)AlSi3O8·0.5(H2O)
P21 or P21/m Mono
|
| |
- Sanidine (K,Na)(Si,Al)4O8 C2/m 2/m
|
| |
Microcline KAlSi3O8 C1- -1 |
| |
- Orthoclase KAlSi3O8 C2/m 2/m
|
| |
- Celsian BaAl2Si2O8 I21/c 2/m
|
| |
- Hyalophane (K,Ba)Al(Si,Al)3O8 C2/m
2/m
|
| |
- Paraselsian BaAl2Si2O8 P21/c
2/m
|
|
|
- Slawsonite (Sr,Ca)Al2Si2O8
P21/a 2/m
|