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Eucryptite
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Eucryptite was named in 1880 by Brush and Dana from the Greek for "well concealed", in allusion to its occurrence embedded in albite.

Discovered in 1880;   IMA status: Valid (pre-IMA; Grandfathered) (IMA approved 19)

Chemistry

Chemical Formula:

LiAlSiO₄

Lithium Aluminum Silicate

Molecular Weight:

126.01 gm

Composition:

Lithium

5.51 %

Li

11.86 %

Li₂O

Aluminum

21.41 %

Al

40.46 %

Al₂O₃

Silicon

22.29 %

Si

47.68 %

SiO₂

Oxygen

50.79 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/A.01-30

Nickel-Strunz 10th Ed. ID:

9.AA.05

9 : SILICATES (Germanates)
A : Nesosilicates
A : Nesosilicates without additional anions; cations in tetrahedral [4] coordination

Related to:

Phenakite Group

Synonyms:

Lithionnephelin

Crystal Data

Crystallography:

Trigonal - Rhombohedral

Crystal Habit:

Rare euhedral crystals, to 3 cm; common forms are {1010}, {1120} and {0001}. In coarse crystalline aggregates and massive.

Twinning:

None

Physical Properties

Cleavage:

{1010} Indistinct, {0001} Indistinct

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

6.5

Density:

2.657 - 2.666 (g/cm³)

Luminescence:

Fluoresces pink to magenta-red or orange under SW UV

Radioactivity:

Not Radioactive

Optical Properties

Color:

Colorless, White, Tan, Gray

Transparency:

Transparent to Translucent

Luster:

Vitreous

Refractive Index:

1.570 - 1.587  Uniaxial ( + )

Birefringence:

0.0130

Pleochroism:

None

Occurances

Geological Setting:

In lithium-rich pegmatites, often as graphic intergrowths with albite derived from alteration of spodumene.

Common Associations:

Albite, Amblygonite, Lepidolite, Petalite, Quartz, Spodumene

Common Impurities:

Na, K

Type Locality:

Abija N. Fillow Quarry (Branchville Quarry), Branchville, Redding, Fairfield Co., Connecticut, USA

Year Discovered:

1880

View mineral photos:

Eucryptite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Eucryptite is a rare silicate mineral and is one of very few silicate minerals that have a trigonal symmetry. It is a member of the Phenakite Group of minerals that includes Eucryptite, Phenakite and Willemite. All three have the same basic chemical structure and symmetry, but different metal ions. Eucryptite can fluoresce a beautiful magenta red to orange under shortwave UV light.

Eucryptite can be found in the USA, from Branchville, Fairfield County, Connecticut; Center Strafford, Strafford County, New Hampshire; in the Harding pegmatite, Dixon, Taos County, New Mexico; in the Midnight Owl pegmatite, Maricopa County, Arizona; and in the Foote mine, Kings Mountain, Cleveland County, North Carolina. From the Tanco pegmatite, Bernic Lake, Manitoba, and near Nakina, Ontario, Canada. In Zimbabwe, large amounts at Bikita, with many other minor localities. From the Haapaluoma quarry, near Peräseinäjoki, Finland.
 

  
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