Moonstone Feldspar

Moonstone may be the opalescent number of orthoclase, having a blue or white sheen (or “schiller”), rather such as the shine from the moon after which it it is known as. This really is brought on by the reflection of sunshine in the internal structure, comprised of alternating layers of albite and orthoclase feldspar. Thin albite layers give a stylish blue; thicker layers create a white “schiller”. Stones of huge size and high-quality are rare.
The very best material is from Burma and Sri Lanka. Other localities include India, Madagascar, Brazil, the united states, Mexico, Tanzania and also the European Alps.

Properties

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.

Classification / Type: 

-

Colors / Varieties: 

Orthoclase: Moonstone (all colors); Transparent: yellow, pink and white; Phenomena: sheen, chatoyancy, asterism, adularescence (blue sheen)

Crystal System / Forms: 

Monoclinic System

Hardness: 

6

Specific Gravity: 

2.55 - 2.63

Cleavage / Fracture: 

Easy 2 directional / Uneven.

Optic Character: 

Anisotropic, D.R.; Biaxial negative

Lustre: 

Vitreous.

Refractive Index / Birefringence: 

1.518 - 1.526 / 0.008

Pleochroism: 

Not common.

Dispersion: 

0.012

Magnification: 

Fine stress cracks parallel to cleavage directions known as centipede inclusions, fingerprints and crystal inclusions.

U.V. Fluorescence: 

Pink under shortwave commonly, variable.

Spectrum: 

Not characteristic.

Cause of Color: 

Color due to impurities, adularescence and sheen due to scattering or light.

Treatment (Enhancement): 

None.

Specific Tests & Remarks: 

-

Synthesis: 

None.

Simulants (with key separation tests): 

• Moonstone from chalcedony (structure, phenomena); glass (inclusions); opal (R.I., S.G.)
• Transparent orthoclase from quartz (optic figure); scapolite (optic figure); petalite (S.G., U.V. fluorescence), glass (optic character, inclusions, U.V. fluorescence)

Geological Occurrence: 

Igneous rocks, pegmatite.

Sources: 

Sri Lanka, Myanmar, India, Madagascar, U.S.A., Tanzania.

Cuts & Uses: 

Facetted, cabochon, beads and carving.