Fluor-Liddicoatite (formerly Liddicoatite)
Current inventory:  1 gem
 

  
Liddicoatite is named for Richard T. Liddicoat (1918-2003), gemologist, who invented the diamond grading system, for his many contributions to the Gemological Institute of America.

Discovered in 1976;   IMA status:  Valid (IMA approved: Redefined Approved 2011)

Chemistry

Chemical Formula:

Ca(Li₂Al)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH)F

Calcium Lithium Aluminum Bora-silicate Hydroxide Fluoride Oxide

Molecular Weight:

917.49 gm

Composition:

Sodium

0.75 %

Na

1.01 %

Na₂O

Lithium

1.21 %

Li

2.61 %

Li₂O

Calcium

3.06 %

Ca

4.28 %

CaO

Aluminum

18.23 %

Al

34.45 %

Al₂O₃

Silicon

18.37 %

Si

39.29 %

SiO₂

Boron

3.53 %

B

11.38 %

B₂O₃

Hydrogen

0.32 %

H

2.38 %

H₂O

Oxygen

52.66 %

O

Fluorine

1.86 %

F

-  %

F

-0.78 %

-0=F₂

100.00 %

96.95 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/E.19-80

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. The F-analogue of Liddicoatite.

Members of Group:

Tourmaline Group: Buergerite, Chromdravite, Chromo-aluminopovondraite, Dravite, Elbaite, Feruvite

Varieties:

None

Synonyms:

IMA1976-041

Crystal Data

Crystallography:

Trigonal - Ditrigonal Pyramidal

Crystal Habit:

Crystals stout prismatic, with curved convex trigonal outline, deeply striated || [0001], to 25 cm.

Twinning:

None

Physical Properties

Cleavage:

Poor on {0001}

Fracture:

Irregular/Uneven to Conchoidal

Tenacity:

Brittle

Moh's Hardness:

7.5

Density:

3.02 (g/cm³)

Luminescence:

Not Fluorescent

Radioactivity:

Not Radioactive

Optical Properties

Color:

Brown, Green, Pink, Red, Blue; commonly zoned parallel to pyramid faces.

Transparency:

Transparent to Translucent

Luster:

Vitreous on fractures

Refractive Index:

1.621 - 1.637  Uniaxial ( - ) 

Birefringence:

0.016

Dispersion:

n/a

Pleochroism:

Strong; O = dark brown; E = light brown

Occurances

Geological Setting:

Detrital in soil, an apparent product of the local pegmatites.

Common Associations:

Quartz, Elbaite, Albite, Micas

Common Impurities:

Mn, Fe, Ti, Mg, Na, H₂O

Type Locality:

Near Antsirabé, Vakinankaratra Region, Antananarivo Province, Madagascar

Year Discovered:

1976 (Redefined Approved 2011)

View mineral photos:

Fluor-Liddicoatite Mineral Photos and Locations

More Information

Mindat.org (Fluor-Liddicoatite)
Mindat.org (Liddicoatite)
Webmineral.com (Liddicoatite)

Liddicoatite was originally thought to be Elbaite (Tourmaline) but upon further investigation it was discovered to be the calcium rich analog of Elbaite and in 1977 approved by the IMA as a new mineral. In 2011 Henry et al. determined that the material from the Type Locality is Fluorine (F) dominant instead of OH-dominant so the type material has been redefined as Fluor-Liddicoatite and "Liddicoatite" is currently a non-approved species name. I'm guessing most gem collectors will continue to call it Liddicoatite.

The only known locations for Fluor-Liddicoatite are Antsirabe, Tsilaizina, and Anjanabonoina, Madagascar. There are probably other localities but chemical analysis is required for distinction from other Tourmaline Group minerals. Liddicoatite is found in a wide variety of colors and crystals are often concentrically zoned or banded with many different colors, usually triangular in outline.
 

  
Liddicoatite gems for sale: