The Very Highest Quality Feldspar Information... |
Feldspar |
|
Feldspar Types
Colour:
The most desired colour of moonstone is blue, but it also occurs in grey, pink, green and brown. Amazonite is green, labradorite is usually blue. Sunstone, sometimes called aventurine feldspar, is yellow to red. There is also a yellow form of orthoclase gemstone, which owes its colour to the presence of iron.
More About Plagioclase
We have stated above that plagioclase is an isomorphous series of albite and anorthite. Mineralogists have given names to minerals falling within certain bands. The following table gives these names and shows the percentages of albite and anorthite which constitute each variety.
Plagioclase Varieties
Variety | Albite % | Anorthite % |
Albite | 90 - 100 | 0 - 10 |
Oligoclase | 70 - 90 | 10 - 30 |
Andesine | 50 - 70 | 30 - 50 |
Labradorite | 30 - 50 | 50 - 70 |
Bytownite | 10 - 30 | 70 - 90 |
Anorthite | 0 - 10 | 90 - 100 |
Characteristics
Chemical Composition and name - Orthoclase & Microcline | KAlSi3O8 - Potassium Aluminium Silicate |
Chemical Composition and name - Albite | NaAlSi3O8 - Sodium Aluminium Silicate |
Chemical Composition and name - Anorthite | CaAl2Si2O8 - Calcium Aluminium Silicate |
Chemical Composition and name - Celsian | BaAl2Si2O8 - Barium Aluminium Silicate |
Hardness | 6 - 6.5 |
Specific Gravity - Orthoclase | 2.55 - 2.58 |
Specific Gravity - Microcline | 2.54 - 2.57 |
Specific Gravity - Oligoclase | 2.62 - 2.65 |
Specific Gravity - Labradorite | 2.70 - 2.72 |
Crystalline System - Orthoclase | Monoclinic |
Crystalline System - Microcline | Triclinic |
Crystalline System - Oligoclase | Triclinic |
Crystalline System - Labradorite | Triclinic |
Refractive Index - Orthoclase | 1.52 - 1.53 to 1.53 - 1.54 |
Refractive Index - Microcline | 1.52 - 1.53 |
Refractive Index - Oligoclase | 1.54 - 1.55 |
Refractive Index - Labradorite | 1.56 - 1.57 |
Bi-refringence - Orthoclase & Microcline | 0.008 |
Bi-refringence - Sunstone & Labradorite | 0.001 |
Optic Sign - Orthoclase, Sunstone, Microcline | Negative |
Optic Sign - Labradorite | Positive |
Optical Character | Biaxial |
Dispersion | 0.012 |
...at the Lowest Possible Price |
32 - 36 Harrowside, Blackpool, Lancashire, FY4 1RJ, England. Telephone (44) - (0) 1253 - 343081 ; Fax 408058; E-mail: The URL for our main page is: https://24carat.co.uk | Chard(1964) Ltd |