Achroite (variety of Elbaite Tourmaline)
Current inventory:  0 gems
 

  
The name Achroite is from the Greek word achro meaning without color. The name Tourmaline is from the Singhalese word tourmali, meaning mixed colored stones because Tourmalines were often confused with other gems, especially Zircon gems.

Discovered in the 1840's;   IMA status: Not Valid (variety of Elbaite Tourmaline)

Chemistry

Chemical Formula:

NaLi_2.5Al_6.5(BO₃)₃O₁₈(OH)₄   (Elbaite)

Sodium Lithium Aluminum Boro-Silicate Hydroxide (Elbaite)

Molecular Weight:

916.68 gm (Elbaite)

Elbaite Composition:

Sodium

2.51 %

Na

3.38 %

Na₂O

Lithium

1.89 %

Li

4.07 %

Li₂O

Aluminum

19.13 %

Al

36.15 %

Al₂O₃

Silicon

18.38 %

Si

39.33 %

SiO₂

Boron

3.54 %

B

11.39 %

B₂O₃

Hydrogen

0.44 %

H

3.93 %

H₂O

Oxygen

54.11 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/E.19-10

Nickel-Strunz 10th Ed. ID:

9.CK.05

9 : SILICATES (Germanates)
C : Cyclosilicates
K : [Si₆O₁₈]₁₂- 6-membered single rings, with insular complex anions

Related to:

Tourmaline Group. Elbaite-Liddicoatite Series. Dravite-Elbaite Series. Elbaite-Schorl Series.

Members of Group:

Tourmaline Group: Buergerite, Chromdravite, Dravite, Elbaite, Feruvite, Fluor-Dravite, Foitite, IMA2009-088, Liddicoatite, Luinaite-(OH), Magnesiofoitite, Olenite, Oxy-Dravite, Oxy-Rossmanite, Povondraite, Rossmanite, Schorl, Uvite, Vanadiumdravite.

Varieties:

None

Synonyms:

Acroite

Crystal Data

Crystallography:

Trigonal - Ditrigonal Pyramidal

Crystal Habit:

Crystals prismatic to acicular, with prominent trigonal prism and pyramid, to 1.6 m, commonly hemimorphic. Also radial, fibrous, and massive.

Twinning:

Rare on {1011} and {4041}

Physical Properties

Cleavage:

[1120] & [1011] Poor, Indistinct

Fracture:

Uneven to Conchoidal

Tenacity:

Brittle

Moh's Hardness:

7.0 - 7.5

Density:

2.90 - 3.10 (g/cm³)

Luminescence:

Fluorescent; weak blue white to blue under SW UV

Radioactivity:

Not Radioactive

Other:

Piezoelectric, Pyroelectric

Optical Properties

Color:

Colorless

Transparency:

Transparent to Translucent

Luster:

Vitreous to Resinous

Refractive Index:

1.615 - 1.651  Uniaxial ( - ); under strain may show slight Biaxiality

Birefringence:

0.0180 - 0.0200

Dispersion:

0.017

Pleochroism:

Colorless

Occurances

Geological Setting:

In granites, granite pegmatites, and some metamorphic rocks; in high-temperature hydrothermal veins; detrital in sediments.

Common Associations:

Quartz, Albite, Lepidolite, Microcline, Garnet, Muscovite, Beryl, Apatite, Spodumene

Common Impurities:

None

Elbaite Type Locality:

Fonte del Prete, San Piero in Campo, Elba Island, Livorno Province, Tuscany, Italy

Year Discovered:

in the 1840's (mentioned on page 266 in Manual of Mineralogy by James Nicol, 1849)

View mineral photos:

Achroite Mineral Photos and Locations
Elbaite Mineral Photos and Locations

More Information

Mindat.org  (Achroite)
Mindat.org  (Elbaite)
Webmineral.com  (Elbaite)

Achroite is the rare colorless variety of Elbaite which is a member of the Tourmaline Group of minerals. Tourmaline is the name given to a family of related minerals, all having the same basic crystal structure but varying widely in chemical composition. Tourmaline comes in all colors including colorless (Achroite) and black (Schorl) with many names given to the many other colors. Colorless tourmaline can also be made by applying heat to light pink tourmalines. Piezoelectric and pyroelectric effects are present in Tourmaline.

Achroite occurs with colored tourmalines within the pegmatites of Madagascar and Pala district, San Diego County, California, USA. Achroite has also been found in Afghanistan, Bolivia, Czech Republic, England, India, Nepal and Sri Lanka.
 

  
Achroite gems for sale:

We have not photographed the Achroite gems yet. Please check back soon.