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ORTHOCLASE                               NATURAL COLOR                              Hardness 6
Next pages  »»  ORTHOCLASE 2 ¦ ORTHOCLASE 3 ¦ ORTHOCLASE SMALL
  Enlarge  21.14 cts. yellow orthoclase oval cut single 

21.5 x 15.5 mm. Depth: 11.4 mm.

  Eye clean. Enhancement: none (N) Untreated

stone PRICE  

USD 890.00 

ORIGIN: Madagascar

ref:Oyo 2114 

 

  Enlarge  30.70 cts. yellow orthoclase round single 

20.5 mm. Depth: 14.1 mm.

  Eye clean. Enhancement: none (N) Untreated

stone PRICE  

USD 1442.00 

ORIGIN: Madagascar

ref:Oyr 3070 

 

Enlarge   66.2 cts. yellow orthoclase emerald cut single 

27.75 x 23.3 mm. Depth: 15 mm.

Slightly included. Enhancement: none (N) Untreated

stone PRICE  

USD 2990.00 

ORIGIN: Madagascar

ref:Oye 6620 

 

   10.35 cts. yellow orthoclase emerald cut single 

15.2 x 11.1 mm.

 Eye clean. Enhancement: none (N) Untreated

stone PRICE  

USD 259.00 

ORIGIN: Madagascar

ref: Oye1035  

 

   9.41 cts. yellow orthoclase emerald cut single 

18.3 x 10 mm.

 Eye clean. Enhancement: none (N) Untreated

stone PRICE  

USD 235.00 

ORIGIN: Madagascar

ref: Oye941 

 

   9.50 cts. yellow orthoclase emerald cut single 

14.4 x 11.1 mm.

 Eye clean. Enhancement: none (N) Untreated

stone PRICE  

USD 238.00 

ORIGIN: Madagascar

ref: Oye950  

 

   8.26 cts. yellow orthoclase oval cut single 

15.1 x 12 mm. "Sugf cut"

 Eye clean. Enhancement: none (N) Untreated

stone PRICE  

USD 209.00 

ORIGIN: Madagascar

ref:Oyo826  

 

   9.54 cts. yellow orthoclase oval cut single 

16 x 11.6 mm.

 Eye clean. Enhancement: none (N) Untreated

stone PRICE  

USD 239.00 

ORIGIN: Madagascar

ref:Oyo954  

 

   10.91 cts. yellow orthoclase round single 

14.2  mm. "Sugf cut"

 Eye clean. Enhancement: none (N) Untreated

stone PRICE  

USD 273.00 

ORIGIN: Madagascar

ref:Oyr1091  

 

  Enlarge  19.96 cts. yellow orthoclase emerald cut single 

18.8 x 15.7 mm. Depth: 10.2 mm.

  Eye clean. Enhancement: none (N) Untreated

stone PRICE  

USD 889.00 

ORIGIN: Madagascar

ref:Oye 1996 

 

  Enlarge  31.03 cts. yellow orthoclase oval single 

21.1 x 16 mm. Depth: 14 mm.

  Slightly included. Enhancement: none (N) Untreated

stone PRICE  

USD 1458.00 

ORIGIN: Madagascar

ref:Oye 3103 

Next pages »»  ORTHOCLASE 2 ¦ ORTHOCLASE 3 ¦ ORTHOCLASE SMALL
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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
 
 
 
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