IMA 2003-032 = lafossaite

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Marco E. Ciriotti
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IMA 2003-032 = lafossaite

Messaggio da Marco E. Ciriotti » mer 25 ago, 2004 13:06

Il nome di questo nuovo "minerale tipo" italiano è stato anticipato sul CD "Italian Type Minerals" previa autorizzazione degli autori.
Poichè il CD ROM è stato regolarmente distribuito ai convenuti del Congresso Internazionale di Geologia di Firenze il nome è ora di pubblico dominio.
La fase, con formula Tl(Cl,Br) - strettamente correlata al sale ammonico - è stata trovata al Cratere La Fossa, Vulcano, Vulcano Island, Lípari, Isole Eólie, Messina, Sicilia, Italia.
Marco E. Ciriotti

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Messaggio da Marco E. Ciriotti » ven 05 nov, 2004 18:03

Sul CD è anche una foto (ben rappresentativa del composto) cortesemente propostaci dall'autore senior Andy C. Roberts.
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Messaggio da Marco E. Ciriotti » gio 20 apr, 2006 15:43

La descrizione-tipo della lafossaite è ora pubblicata.

Referenza:
• Roberts, A.C., Venance, K.E., Seward, T.M., Grice J.D., Paar, W.H. (2006): Lafossaite a new mineral from the La Fossa Crater, Vulcano, Italy. Mineralogical Record, 37, 165-168.
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Messaggio da Marco E. Ciriotti » gio 20 apr, 2006 16:08

La specie era stata rinevnuta in passato (unnamed TlCl) in granuli 1-12 micron nella kimberlite diamantifera di Udachnaya, Saha Federal Republic (ex Yakutia), Russia.

Ma ci saranno altre novità...

Referenza:
• Gorshkov, A.I., Vinokurov, S.F., Solodov, D.I., Bershov, L.V., Mokhov, A.V., Solodova, Yu.P., Sivtsov, A.V. (1998): Polycrystalline diamond from the Udachnaya Pipe, Yakutia: mineralogical, geochemical, and genetic characteristics. Lithology and Mineral Resources, 33, 525-538.


La struttura del composto equivalente sintetico è nota sin dal 1921.

Referenza:
• Davey, W.P. & Wick, F.G. (1921): The crystal structure of two rare halogen salts. Physical Review, 17, 403-404.
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Messaggio da Marco E. Ciriotti » gio 20 apr, 2006 17:04

Ecco un breve abstract (cortesemente redatto da Jim Ferraiolo):

Lafossaite occurs as a drusy coating on one surface of a single specimen collected from one of the active 400°C fumaroles on the rim of the La Fossa crater, on the island of Vulcano in the Aeolian archipelago, Sicily. The grey-brown euhedral to subhedral crystals form cubes and ocahedra which do not exceed 0.2 mm in size and are tightly intergrown in some areas; they have a resinous to greasy luster, H = 3–4, Dcalc. 7.212 g/cm3; soluble in dilute HCl; yellow-brown in plane-polarized light, isotropic, with n >> 1.8 (ncalc= 2.264 at 589 nm); reflectance ~ 15% in air (4% in oil). EPMA gave Tl= 81.74, Cl= 10.79, Br= 5.99,total = 98.52, leading to the idealized formula TlCl. Indexed XRD powder data are tabulated; strongest lines 2.745(100), 3.887(80).1.583(70), 2.237(55), 1.937(50) Å; a 3.8756 Å, V 58.213 Å3, Z = 1, space group Pm3m. Lafossaite formed directly from fumarolic gas and is associated with a number of other sublimate minerals including cannizzarite, galenobismutite, pyrite and an unidentified Fe-K-Si-bearing phase. The name is for the locality.
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Messaggio da Marco E. Ciriotti » mer 31 mag, 2006 11:18

Ed ora un abstract un pochino più completo.

Referenza:
• Roberts, A.C., Venance, K.E., Seward, T.M., Grice J.D., Paar, W.H. (2006): Lafossaite a new mineral from the La Fossa Crater, Vulcano, Italy. Mineralogical Record, 37, 165-168.

Abstract:
Lafossaite, idealized formula TlCl, is cubic, space group P-m3m (by analogy with the synthetic inorganic equivalent) with unit-cell parameter refined from powder data: a = 3.8756(3) Å, V = 58.213(8) Å^sup 3^, Z = 1. The strongest six reflections in the X-ray powder-diffraction pattern are [d(Å)(I)(hkl)]: 3.887(80)(100); 2.745(100)(110); 2.237(55)(111); 1.937(50)(200); 1.733(45)(210); 1.583(70)(211). The mineral occurs on a single specimen (6 × 7 × 9 cm) collected from one of the active 400°C fumaroles on the rim of the La Fossa crater, island of Vulcano, Aeolian archipelago, Sicily, Italy, as a drusy coating on one surface. The mineral formed as a sublimate directly from fumarolic gas and is associated with a number of other sublimate minerals including cannizzarite, galenobismutite, pyrite and an undefined Fe-K-Si-bearing phase. Crystals do not exceed 0.2 mm in size and are euhedral to subhedral (predominant) cubes and octahedra which are tightly intergrown in some areas. Forms are {100} (smooth and lustrous) major, {111} (rough and non-lustrous) minor, and {110} (rough and non-lustrous) very minor. Lafossaite possesses the following physical properties: color is gray-brown (R.H.S. 199D); streak is off-white to cream (and resinous looking); luster is resinous to greasy; diaphaneity is translucent; non-fluorescent; Mohs hardness is estimated at 3-4; tenacity is malleable; fracture is subconchoidal; cleavage and parting are not evident; calculated density is 7.212 g/cm^sup 3^ (for empirical formula and unit-cell parameter refined from powder data). The mineral is yellow-brown in plane-polarized transmitted light, isotropic with no pleochroism, and n[much greater than]1.8. In plane-polarized reflected light, it is grayish-white, with white internal reflections and no evidence of anisotropy, bireflectance or pleochroism. The calculated index of refraction (589 nm) is 2.264. Reflectance values, in air and in oil, are tabulated. Averaged electron-microprobe analyses: Tl = 81.74, Cl = 10.79, Br = 5.99, total = 98.52 weight %, corresponding to Tl^sub 1.03^(Cl^sub 0.78^Br^sub 0.19^)^sub Σ0.97^, based on 2 total atoms. The mineral is soluble in dilute HCl. The mineral name is for the locality.
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