AEGERINE AUGITE

Chemical Formula : (Na, Ca) (Fe⁺², Fe⁺³, Mg, Al) Si₂ O₆

Composition : Calcium Magnesium Iron Aluminium Silicate

Crystal System : Monoclinic

Group : Pyroxene - Ino silicates

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3D MODEL

Physical Properties

Color : Dark green to black green

Form / Habit : Prismatic

Cleavage : Good prismatic Cleavage

Hardness : 5 - 6

Specific Gravity : 3.5

Fracture : Conchoidal to splintery

Luster : Vitreous to Resinous

Streak : Grey

Occurrence : It is found in alkaline igneous rocks such as alkaline granite, syenite, phonolite. It is also found in richterite and glaucophane schist.

Uses : It is of considerable interest to petrologists and used as gemstone.

Optical properties

Under parallel nicol

Color : Colourless to pale green

Form : Anhedral, Prismatic

Cleavage : Perfect prismatic cleavage

Fracture : Absent

Relief : High

Refractive index : 1.66-1.76

Pleochroism : Weak to moderate pleochroism. Pale greenish to violet.

Under cross nicol

Nature : Anisotropic

Interference colour : Colours of II order.

Birefringence : Moderate

Extinction : Inclined extinction.

Extinction angle : 35⁰ - 48⁰

Twinning : Absent

Optical character : Biaxial positive

Diagnostic property : Clino pyroxenes are readily identified by their 90° cleavage and inclined extinction. Augite can be distinguished from pigeonite by higher 2V and birefringence. Extinction angle ranges from 35⁰ to 48⁰. Both aegerine and aegerine augite have smaller angles.