A reexamination of the turquoise group: the mineral aheylite, planerite (redefined), turquoise and coeruleolactite

Abstract

The turquoise group has the general formula:A0–1B6(PO4)4−x(PO3OH)x(OH)8.4H2O, wherex= 0–2, and consists of six members: planerite, turquoise, faustite, aheylite, chalcosiderite and an unnamed Fe2+-Fe3+analogue. The existence of ‘coeruleolactite’ is doubtful. Planerite is revalidated as a species and is characterized by a dominantA-site vacancy. Aheylite is established as a new member of the group, and is characterized by having Fe2+dominant in theA-site.Chemical analyses of 15 pure samples of microcrystalline planerite, turquoise, and aheylite show that a maximum of two of the (PO4) groups are protonated (PO3OH) in planerite. Complete solid solution exists between planerite and turquoise. Other members of the group show variableA-site vacancy as well. Most samples of ‘turquoise’ are cation-deficient or are planerite. Direct determination of water indicates that there are 4 molecules of water.Planerite, ideally ☐Al6(PO4)2(PO3OH)2(OH)8.4H2O, is white, pale blue or pale green, and occurs as mamillary, botryoidal crusts as much as several mm thick; may also be massive; microcrystalline, crystals typically 2–4 micrometres, luster chalky to earthy, H. 5, somewhat brittle, no cleavage observed, splintery fracture, Dm2.68(2), Dc2.71, not magnetic, not fluorescent, mean RI about 1.60.a7.505(2),b9.723(3),c7.814(2) Å, α 111.43°, β 115.56°, γ 68.69°, V 464.2(1) Å3, Z = 1.Aheylite, ideally Fe2+Al6(PO4)4(OH)8.4H2O, is pale blue or green, and occurs as isolated and aggregate clumps of hemispherical or spherical, radiating to interlocked masses of crystals that average 3 micrometres in maximum dimension; porcelaneous-subvitreous luster, moderate to brittle tenacity, no cleavage observed, hackly to splintery fracture, not magnetic, not fluorescent, biax. (+), mean RI is about 1.63, Dm2.84(2), Dc2.90.a7.400(1),b9.896(1),c7.627(1) Å, α 110.87°, β 115.00°, γ 69.96°, V 460.62(9) Å3, Z = 1.

The crystal structure of faustite and its copper analogue turquoise

“…Chemical analyses have demonstrated (Pring et al, 2000) that the faustite contains little or no copper and only very small quantities of iron (probably Fe3+ substituting for AI; see Foord and Taggart, 1998). The present article reports the refinement of the crystal structure of one of these faustite crystals.…”

“…Both belong to the turquoise group which also includes the members chalcosiderite, CuFd+(P04MOH)s-4H20, aheylite, (Fe2' ,Zn)AI6(P04MOHk4H20 and planerite, OAI6(P04h(P030Hh(OHk4H20 (0 = vacancy) (see recent review of Foord and Taggart, 1998 for further details). The crystal structure of faustite has not been verified or refined to date, although it was assumed to be isostructural with turquoise, which had been determined to be triclinic, with space group PI (Cid-Dresdner, 1965; R = 7%).…”

New naturally occurring mineral phases from the Krásno - Horní Slavkov area, western Bohemia, Czech Republic

“…The general formula of minerals of the turquoise group is AB 6 (TO 4 ) 4-x (TO 3 OH) x (OH) 8 . 4H 2 O, where x = 02 in dependence on occupancy of the A-site (Foord Taggart 1998). The A-site can be occupied by Cu (turquoise, chalcosiderite), Zn (faustite), Fe 2+ (aheylite) and vacancy (planerite); B-site is occupied dominantly by Al and lesser Fe (chalcosiderite and unnamed Fe 2+ Fe 3+ dominant member); the tetrahedral T-site is occupied in known members of the series always by phosphorus (Foord Taggart 1998).…”

Fosfatos primários e secundários nos perfis de intemperismo sobre os Maciços Alcalino-Carbonatíticos de Juquiá (SP), Anitápolis (SC) e Tapira (MG)

“…Scott (1987) (Schaller, 1912, apud Foord & Taggart Jr., 1998 2b Lynch Station, Virgínia (Foord & Taggart Jr., 1998); 3 planerita -turquesa Dug Hill, Arkansas (Foord & Taggart Jr., 1998 raios-X da turquesa (Foord & Taggart Jr., 1998 Vieillard et al (1979) (Rose efal.,1958, Goetzee & Edwards, 1959, McKie, 1962, Deans, 1966, todos apud Altschuler, 1973 (Florêncio & Toledo, 1997 Segundo alguns autores, a apat¡ta começa a se desestabilizar em ambientes moderadamente ácidos, sendo totalmente dissolvida, em pH de 5,S a 6,5 (Lucas ef a¿, 1980, Flicoteaux & Lucas, 1984, Zanin, 1989 e Lottermoser, 1990, Almeida, 1983 Anitápolís: Kahn, 1988, Pere¡ra, 'l991, Percira et al, '1997, Costa, 1987, Ziesemer& Kahn. , 1980, Furtado, 1989, Vergara, 1980, Hesui & Cordani, 1968 Juquiá: Alcover Neto, 1991, Born, 1971, Walter, lg91, Waltet etal.…”

“…Turquesa: (Cu2*, Ca2*) (Al3*, Fe3)6 (pO1)1 4O2-(anidra), base Al3*+ Fe3*=6, segundo Foord & Taggart (1998 G¡lkes & Palmer ('1983) observaram que cpm o aumento da participação do Sr no sítio A a temperatura de desidratação oscila, diminui de 47O para 420'C de uma crandallita pura para uma crandallita cnm 21o/o molar de Sr e torna a aumentar para 420'C para uma goyazita. Schwab et al (199Oa) Amostras coletadas por Pereira (1991) 1\s --11 ._/ ,t o,oolo.oo4o'oolo'oo8o,oo1o,oo20'0140'o1oo,oo1o'oo,f0'0010,00'10'0540'0400,035 o,oo3o,o12o,oo4o'ooEo,ooo0,006o,oooo'oooo'ool0'0000'0040, Tabela lg Análises à m¡crossonda eletrônica (em % em peso dos óxidos) e cálculos de fórmulas estrutura¡s das apatitas de Anitápolis.…”