Emerald Properties

In the tables below we can see the properties of the emerald and some important data according to its deposits:

PHYSICAL, CHEMICAL AND CRYSTALLOGRAPHIC PROPERTIES

Chemical Formula Al2 Be3 [Si6 O18] + Cr o V
Mineral Type Group IX Silicates
Streak White
Hardness 7.5 – 8 Mohs
Specific Gravity 2.67 – 2.78
Cleavage Imperfect on the [0001]
Fracture Little Conchoidal, uneven, fragile
Crystal System Hexagonal
Habit Hexagonal prism with pinachoidal ending

Source: Compilation of various gemological texts.

OPTICAL PROPERTIES

Optical Properties Uniaxial (-)
Emerald optic sign Negative
Transparency From transparent to opaque
Color Green, yellowish green, bluish green
Luster Vitreous
Refractive Index 1.568 – 1.573  //  1.578 – 1.584
Birefrigerence 0.005  / 0.006
Dispersion 0.014 (BG), 0.009-0.013 (CF)
Pleochroism Green — Blue/Green — Yellow
Fluorenscence LUV: strong red | SUV: weak

Source: Compilation of various gemological texts.

PROPERTIES OF THE EMERALDS ACCORDING TO DEPOSIT

Deposit Refractive Index Birefringence Specific Gravity Fluorescence
Muzo (Colombia) 1.584 – 1.578 0.006 2.71 Red
Chivor (Colombia) 1.577 – 1.571 0.006 2.69 Red
Borbur (Colombia) 1.569 – 1.576 0.007 2.704 Stronge red
Gachalá (Colombia) 1.577 – 1.570 0.007 2.71 Rose
Bahia 1.566 – 1.571 0.005 2.67 – 2.70 Inert
Urals 1.588 – 1.581 0.006 2.72 – 2.74 Rose
Habachthal 1.591 – 1.584 0.007 2.72 -2.76 Inert
Bon Jesus das Meiras 1.574 – 1.569 0.005 2.67 Inert – Rose
Sandawana 1.593 – 1.586 0.007 2.74 – 2.77 Inert
Transvaal 1.593 – 1.586 0.007 2.72 – 2.89 Inert
India 1.593 – 1.586 0.007 2.72 – 2.75 Inert
Australia 1.572 – 1.579 0.007 2.69 Inert
Norway  — 2.68 -2.73 Red

Source: Magazine “Las gemas y otras materias preciosas”, Volume “La Esmeralda”, Instituto Gemológico Español, 1968.