Liddicoatite
Liddicoatite is an unusual person in the tourmaline selection of minerals, elbaite subgroup, in addition to theoretical calcium endmember regarding the elbaite-fluor-liddicoatite series; the pure end-member has not yet been present in nature. Fluor-liddicoatite is indistinguishable from elbaite by X-ray diffraction techniques. A string is made because of it with elbaite and probably also with olenite. Liddicoatite happens to be a mineral this is certainly non-approved, but Aurisicchio et al. (1999) and Breaks et al. (2008) found OH-dominant species. When comes to Crystal habit, its Crystals are stout prismatic, with a curved convex trigonal outline, generally elongated and striated parallel to the axis this is actually c. Crystals are hemimorphic, which means the 2 ends concerning the crystal have different forms. Fluor-liddicoatite usually has a pedion (just one single face that is crystal opposite one or two pyramids
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.
| Category: | Tourmaline Group |
| 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 |
| Crystallography: | Trigonal – Ditrigonal Pyramidal |
| Crystal Habit: | Crystals stout prismatic, with the curved convex trigonal outline, deeply striated || [0001], to 25 cm. |
| Twinning: | None |
| 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 |
| 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 |
