Amazonite

amazonite
Rough amazonite

A form of alkali feldspar, microcline may be colourless, white, yellow, pink, red, grey, green or blue-green. However, the semi-opaque, blue-green variety called amazonite (named after the Amazon River) is most commonly used in jewellery, and may be cut, usually in cabochon, up to almost any size. Its striking colour is a due to the presence of lead.

The most important source of amazonite is in India. Other localities include United States, Canada, the former USSR, Madagascar, Tanzania and Namibia.

Although microcline has the same composition as orthoclase, its crystal structure is triclinic.

Amazonite Pictures

Rough amazoniteAmazonite cabochonAmazonite beads

Cause of Color :

Color due to color centres, aventurescence due to incipient (fine) cleavage cracks.

Chemical Composition :

Aluminum silicate of potassium, sodium and calcium. KAlSi3O8. Isomorphous series made up of Albite (Na), Oligoclase, Andesine, Labradorite, Bytownite and Anorthite (Ca) where the two end member are NaAlSi3O8 and CaAl2Si2O8.

Crystal System / Forms :

Triclinic System

Cuts & Uses :

Facetted, cabochon, beads and carving.

Dispersion : 0.012
Hardness : 6.5
Lustre : Vitreous
Magnification :

Fine incipient cleavage directions giving a silvery sheen effect.

Optic Character :

Anisotropic, D.R.; Biaxial negative

Pleochroism : Not common
Refractive Index / Birefringence :

1.522 – 1.530 / 0.008

Simulants (with separation tests) :

Amazonite from chalcedony (structure, phenomena), turquoise (R.I., S.G., structure), Moonstone (phenomena, structure

Sources :

Brazil, India, Tanzania, Russia, U.S.A., Canada, South Africa, Madagascar.

Spectrum :

Not characteristic

Synthesis :

None

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