Prismatine

Prismatine is a member of the Kornerupine-Prismatine series and closely related to Kornerupine. The chemical formula of Prismatine is  (Mg,Al,Fe)5Al4(Si,Al)4(B,Si,Al)(O,OH,F)22 (Magnesium Aluminum Iron Boron Silicate Oxide Hydroxide Fluoride) and its molecular weight is 755.83 gm. The color is a green that is consistent with Kornerupine but is not pleochroic like Kornerupine. Prismatine has a specific gravity of 3.41 – 3.45 (g/cm3) and refractive index of 1.669 – 1.830 Biaxial ( – ). Moh’s Hardness is 6.5 – 7.0. The material from Tanzania has been sold as Kornerupine but after advanced testing by GIA it was determined that it is actually a related analog to Kornerupine known as Prismatine. The green color is largely due to the Vanadium content.

Although there are several locations for finding Prismatine, the only gem quality crystals have been found in Tanzania.

Category: Sorosilicate
Chemical Formula: (Mg,Al,Fe)5Al4(Si,Al)4(B,Si,Al)(O,OH,F)22
Magnesium Aluminum Iron Boron Silicate Oxide Hydroxide Fluoride
Molecular Weight: 755.83 gm
Composition: 
Magnesium 9.97 % Mg 16.53 % MgO
Aluminum 21.78 % Al 41.14 % Al2O3
Iron 5.91 % Fe 2.85 % FeO / 5.28% Fe2O3
Silicon 14.12 % Si 30.21 % SiO2
Boron 0.86 % B 2.76 % B2O3
Hydrogen 0.40 % H 3.58 % H2O
Oxygen 44.45 % O
Fluorine 2.51 % F 2.51 % F
– – % F -1.06 % -O=F2
  100.00 % 100.00 % = TOTAL OXIDE
 

 

 

Crystallography: Orthorhombic – Dipyramidal
Crystal Habit: Crystals are prismatic.
Twinning: None

 

Cleavage: [110] Perfect  
Tenacity: Brittle
Moh’s Hardness: 6.5 – 7.0
Density: 3.41 – 3.45 (g/cm3)
Luminescence: None
Radioactivity: Not Radioactive
   
 

 

Color: Grayish Green, Greenish Brown, Yellowish Brown
Transparency: Transparent to Translucent
Luster: Vitreous
Refractive Index: 1.669 – 1.830  Biaxial ( – )
Birefringence: 0.013
Dispersion: r > v, Strong
Pleochroism: None