Aquamarine
Aquamarine | |
---|---|
Chemical composition | Be3Al2(SiO3)6 Beryllium aluminum silicate |
Crystal system | Hexagonal |
Habit | Prismatic |
Cleavage | Imperfect, basal, almost never seen |
Hardness | 7.5 to 8 |
Optic nature | Uniaxial - |
Refractive index | 1.577-1.583 (+0.017, - 0.017) |
Birefringence | 0.005-0.009 |
Dispersion | Low, 0.014 |
Specific gravity | 2.72 (+0.18,-0.5) |
Lustre | Vitreous |
Pleochroism | Weak to moderate |
Aquamarine is a pastel greenish-blue variety of the mineral beryl and owes it's color to the presence of iron impurities. Its name is derived from the Latin words for water (aqua) and sea (marine). Crystals form in large hexagonal prisms. In ancient times, it was believed that sailors wearing aquamarine pendants would be protected from the perils of the sea. The stone symbolized happiness and eternal youth. It was viewed in Christian symbolism to bring moderation and control of passions to its owner.
Contents
Beauty is in the eye of the beholder
In the past, the natural greenish-blue color of aquamarine was considered the most desirable. Today, the usual color that we see of Aquamarine is a pale pastel blue. The most sought after color is a deep blue, as typified by the "Santa Maria", "Santa Maria d'Afrique" and "Marta Rocha" aquamarine finds.
Diagnostics
Aquamarine can be confused with Glass, Zircon, Topaz and synthetic Spinel when observed with the unaided eye.
Seperation techniques are given below.
Loupe
Doubling of pavillion facets may be easily detected in Zircon.
Polariscope
Aquamarine, Topaz and Zircon are anisotropic.
Glass and synthetic Spinel are isotropic and can be easily seperated using the polariscope (ADR can occur).
Topaz is biaxial and can be seperated with the use of a conoscope.
Metamict (low-type) Zircon may appear isotropic.
Dichroscope
Glass and synthetic Spinel will show only one color.
Topaz is trichroic.
Aquamarine will show weak to distinct dichroism (green/blue and colorless), Zircon has weak pleochroism which may not be seen in heated blue Zircon.
"True Blue" Aquamarine may show strong dichroism.
Chelsea Colour Filter
Aquamarine: distinct green Glass (paste colored by cobalt): bright red Blue synth. Spinel: orange to red Blue Topaz: greenish Blue Zircon: greenish
Refractometer
Specific Gravity
Treatments
Routinely heat treated, which removes the green cast, leaving only the blue.
Typical inclusions
Rain inclusions