Peridot Education

GENERAL DESCRIPTION

 

 

  • Name: Peridot (gem-quality Olivine), variety of Forsterite (Fayalite – Forsterite Series). Probably, the name is derived from the Arabic word “faridat” – GEM.
  • Formula: (Mg,Fe)2 SiO
  • Crystal system: Orthorhombic
  • Habit: Orthorhombic prism with vertical rhombic faces and side pinacoids
  • Nesosilicate
  • Common Impurities: Fe
  • Genesis: Mafic and ultramafic igneous rocks.
  • Origen: Burma (Myanmar), Sri Lanka, Pakistan, China, Norway, USA, Hawaii, Russia, France, Australia …

 

 Liquid and gas inclusions (lily pads)  

 Liquid inclusions ("feathers")

Negative crystal

PHYSICAL AND OPTICAL PROPERTIES OF BERYL

 

  • Hardness (Mohs): 6½ – 7
  • Cleavage: Poor
  • Fracture: Conchoidal.
  • Colour: Green, Yellow-green, greenish yellow, brownish green, rarely asterism or chatoyancy.
  • Transparency: Transparent, translucent.
  • Streak: White.
  • Lustre: Vitreous, greasy.
  • Dispersion: 0,020
  • Density: 3,34 (± 0,04) g/cm3
  • Forsterite: 3,21 g/cm3
  • Fayalite: 4,00 g/cm3
  • Optic nature: Biaxial +
  • Refractive index: nα = 1.636 - 1.730     nβ = 1.650 - 1.739     nγ = 1.669 - 1.772
  • Birefringence: δ 0,035 – 0,038.
  • Pleochroism: Weak. Yellow-green - green - colorless
  • Fluorescence: Inert
  • Phosphorescence: Null.
  • Absorption spectrum: Three bands in the green-blue and blue (493 nm, 473 nm and 453 nm)
  • Inclusions: Liquid and gas inclusions cause stress cracks (disk-like or “lily pads”), solid inclusions (chromite, ludwigite, mica), negative crystals, biphasic inclusions, strong birefringence (doubled image)
  • Enhancements: is not typically enhanced

 

Fiber inclusions

 

  

Liquid and solid inclusions

 

Strong birefringence 

 

Solid Inclusions and lily Pads (disc-like liquid and gas inclusions)