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 SiO4
- 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 …
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Liquid and gas inclusions (lily pads)
Liquid inclusions ("feathers")
Negative crystal
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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
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Fiber inclusions
Liquid and solid inclusions
Strong birefringence
Solid Inclusions and lily Pads (disc-like liquid and gas inclusions)
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