Fluor-liddicoatite

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Fluor-liddicoatite
Specific gravity
3.02
Optical propertiesUniaxial (−)
Refractive indexNo = 1.637, Ne = 1.621
PleochroismStrong: O dark brown or pink, E light brown or pale pink
Other characteristicsNot fluorescent, not radioactive
References[3][4][5][6]

Fluor-liddicoatite

olenite.[3] Liddiocoatite is currently a non-approved mineral name, but Aurisicchio et al. (1999) and Breaks et al. (2008) found OH-dominant species.[8][9]
Formulae are

  • Fluor-liddicoatite Ca(Li2Al)Al6(BO3)3Si6O18(OH)3F
  • Elbaite Na(Al1.5Li1.5)Al6(BO3)3Si6O18(OH)4
  • Olenite NaAl9B3Si6O27O3(OH)

Fluor-liddicoatite was named in 1977 after Richard T. Liddicoat (1918–2002) gemmologist and president of the Gemological Institute of America,[2] who is well known for introducing the GIA diamond grading system in 1953.

Unit cell

Fluor-liddicoatite belongs to the

unit cell
parameters

Structure

Fluor-liddicoatite is isostructural with (has the same structure as) all members of the

cyclosilicates
with the general formula

  • XY3Z6(BO3)3Si6O18(OH,O)3(OH,F).

For fluor-liddicoatite, the X sites are occupied by Ca, the Y sites by Li or Al and the Z sites by Al, giving the formula

  • Ca(Li2Al)Al6(BO3)3Si6O18(OH)3F.

The Y sites are

aluminum Al ions at the Z sites, and its outer oxygen atoms are also atoms of the aluminum coordination octahedra. The X sites are sandwiched between the units along the c axis.[10][11]

Crystal habit

Crystals are stout

trigonal outline, generally elongated and striated parallel to the c axis. Crystals are hemimorphic, meaning that the two ends of the crystal have different forms. Fluor-liddicoatite usually has a pedion (a single crystal face) opposite one or two pyramids.[3]

Physical properties

A polished slice of liddicoatite from Madagascar. Photo Rob Lavinsky

The color is usually smoky brown, but also pink, red, green, blue, or rarely white. Color zoning is abundant at the type locality, parallel to pyramid faces. This is due to changes in the solution during crystal growth. As the concentration of trace elements that serve as coloring agents changes, there will be areas of less or more color in different parts of the crystal. When the crystal is sliced perpendicular to the c axis, triangular zoning may be seen, together with a trigonal star that radiates from the centre of the crystal, with the three rays directed towards the corners of the triangular color patterns.[12]
The pink-red color is due to the manganese Mn3+ content, and the green color is due to intervalence charge transfer transactions between iron Fe2+ and titanium Ti4+.[12]
The streak is white to very light brown, lighter than the mass color, luster is vitreous and crystals are transparent to translucent.

Specific gravity is 3.02, a little lighter than fluorite. It is neither fluorescent nor radioactive
.

Optical properties

Fluor-liddicoatite is uniaxial (-), with refractive Indices No = 1.637 and Ne = 1.621 for the type specimen. The refractive indices, however, will vary from specimen to specimen, as they depend on the content of iron and manganese, which are usually present as trace elements.[2] Pleochroism is strong: O dark brown or pink, E light brown or pale pink.

Environment

Fluor-liddicoatite is

micas.[6]

Localities

Luc Yen
, Vietnam. Size: 8.5 x 7.6 x 4.7 cm.

The type locality is Anjanabonoina, Tsilaizina, Antsirabe, Madagascar.[3] Type Material is stored at the National Museum of Natural History, Smithsonian Institution, Washington, D.C., US, catalogue #135815; further type material is stored at the Natural History Museum, London, the Royal Ontario Museum, Canada and the Geological Survey of Canada.[2]

  • Deep brilliant red, highly lustrous, prismatic fluor-liddicoatite has been found as large sheaves of near parallel, slightly divergent crystals, at the Minh Tien pegmatite,
    Luc Yen District, in Vietnam.[13]
  • At Ambalabe, Manapa, near
    londonite.[14]
  • In Tsarafara in the Sahatany Valley,
    Vakinankaratra Region, Madagascar, striated, lustrous, gemmy, color-zoned fluor-liddicoatite crystals have been found. Most of these have red tips and green middle zones, some with as many as five distinct color bands. Some of the crystals rest on greyish quartz.[14]

References

  1. S2CID 235729616
    .
  2. ^ a b c d e f g American Mineralogist (1977) 62:1121
  3. ^ a b c d e f g h Gaines et al (1997) Dana’s New Mineralogy. Wiley
  4. ^ a b c "Liddicoatite". www.mindat.org.
  5. ^ a b c "Liddicoatite Mineral Data". www.webmineral.com.
  6. ^ a b c d "Liddicoatite" (PDF). University of Arizona. Mineral Data Publishing. 2001. Archived (PDF) from the original on 2006-09-05.
  7. S2CID 38696645. Archived from the original
    (PDF) on 2012-03-26. Retrieved 2012-04-18.
  8. doi:10.1127/ejm/11/2/0237.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  9. ^ Breaks, F.W.; Tindle, A.G. & Selway, J.B. (2008). Electron microprobe and bulk rock and mineral compositions from rare-element pegmatites and peraluminous, S-type granitic rocks from the Fort Hope pegmatite field, north-central Superior Province of Ontario. Vol. 235. Ontario Geological Survey, Miscellaneous Release Data.
  10. ^ a b Deer, Howie and Zussman (1986) Rock-forming minerals, (2nd edition), Volume 1B, Disilicates and Ring Silicates
  11. ^ American Mineralogist (1948) 33:532
  12. ^ a b extraLapis English No 3: Tourmaline (2002)
  13. ^ The Mineralogical Record (2006) 37-5:482
  14. ^ a b The Mineralogical Record (2007) 38-3:220

External links

Wikimedia Commons has media related to Fluor-liddicoatite.
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