Name:

Andalusite

Chem:

Al2SiO5
Aluminum Silicate

Crystal:

Orthorhombic (Large size gem quality crystals are rare.)

 

Color:

Strong pleochroism one axis/yellow-olive other axis/brown-red

Refrac. Index:

1.63 - 1.648

Birefraction:

0.006

Hardness:

7.5 (gem quality)

Spec. Grav.:

3.12 - 3.18

Fracture:

conchoidal

Cleavage:

imperfect

Environment:

Found in pegmatites, gneiss, hydrothermal deposits, and gem gravel

Association:

quartz, muscovite, microcline, cordierite, topaz

Locals:

| Brazil | Sri Lanka | Canada | Spain |

Misc:

the name is from a region in Spain (Andalucia), it is one member of three minerals with the same composition, andalusite, sillmanite, and kyanite.

Gem info:

It is mainly a collectors item, and has not seen wide use in the jewelry trade, there is another variety called chiastolite that forms long prismatic crystals with a black cross in its cross section. The name comes from the Greek "chiastos" meaning "X-marked". It was used as an amulet by early Christens.

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pendant