Tzeferisite
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7 : Sulfates (selenates, tellurates, chromates, molybdates, wolframates)
D : Sulfates (selenates, etc.) with additional anions, with H2O
| Tzeferisite | |
|---|---|
 Damianos Mine, Dimoliaki mines, Dimoliaki, Lavrion Mining District, Lavreotiki, East Attica, Attica, Greece (Lavrion Type locality) | |
| General | |
| Category | Sulfate mineral |
| Formula | CaZn8(SO4)2(OH)12Cl2(H2O)9 |
| IMA symbol | Τze[1] |
| Strunz classification | 7.DF.
7 : Sulfates (selenates, tellurates, chromates, molybdates, wolframates) |
| Crystal system | Trigonal |
| Crystal class | 3m (3 2/m) - Hexagonal Scalenohedral |
| Space group | R3c |
| Unit cell | 4,112.46 Å3 |
| Identification | |
| Colour | White, colorless |
| Lustre | Vitreous |
| Diaphaneity | Transparent |
| Other characteristics | Tzeferisite is not radioactive |
Tzeferisite is a sulfate mineral with formula CaZn8(SO4)2(OH)12Cl2(H2O)9. It is the natural analog of the anthropogenic slag phase Ca0.5Zn4(SO4)(OH)6Cl·4.5H2O that was first discovered in slag dumps at Val Varenna, Italy (formula halved and reformulated to show the similarities to the other compounds discussed; (Burns et al., 1998)
Gordaite, NaZn4(SO4)(OH)6Cl·6H2O (Adiwidjaja et al., 1997; Zhu et al., 1997) and Fabritzite Zn0.5Zn4(SO4)(OH)6Cl·3H2O (formula halved and reformulated to show the difference between the two octahedrally Zn atoms), are closely related. All three compounds share the same brucite-type octahedral sheet with attached Zn (OH)3Cl tetrahedra, only the charge-balancing interlayer cation is different (0.5Zn2+ vs Na+ and 0.5Ca2+, respectively).[2]
Tzeferisite is a supergene mineral, member of Namuwite Group. Chlorine-rich solutions that caused the leaching of Cd from primary sphalerite and the deposition of secondary, fine-grained greenockite were also responsible for the deposition of tzeferisite. Associated minerals include sphalerite, galenite, greenockite, hemimorphite, fabritzite, gypsum, calcite, and dolomite.
[επεξεργασία] Tzeferisite forms thin, colorless to white, hexagonal platelets (up to 250 μm in diameter and up to 25 μm thick) that are aggregated in clusters or evenly distributed on the matrix. It is white or colorless with a vitreous luster. The "yellow" impression often seen is due to the greenockite-bearing matrix or due to microinclusions of greenockite in tzeferisite itself. Associated minerals are sphalerite, galenite, greenockite, hemimorphite, fabritzite, gypsum, calcite, dolomite.[3]
Table 1: Chemical data (in wt%) for tzeferisite*.
| Constituent | % weight | |
|---|---|---|
| Zn | 43.865 | |
| O | 38.913 | |
| Cl | 5.947 | |
| S | 5.378 | |
| Ca | 3.361 | |
| H | 2.536 |
* Calculated from ideal end-member formula.
Chemical analysis by electron microprobe resulted in the empirical formula Ca0․99Zn8․02(SO4)2(OH)12Cl1․98(H2O)9, calculated on the basis of 30 H atoms per formula unit (apfu). The simplified formula is CaZn8(SO4)2(OH)12Cl2(H2O)9
The ideal formula is CaZn8(SO4)2(OH)12Cl2(H2O)9, which requires SO3 13.43 wt.%, H2O 22.66 wt.%, CaCl2 9.31 wt.%, ZnO 54.60 wt.%, Total 100 wt.%.
The mineral tzeferisite from the Lavrion mining district, Attica, Greece and the synthetic compound from the slag dumps at val Varenna, Italy exhibit the same crystal structure. Crystal data for tzeferisite, space group R3c, are listed on the right table. Unit cell dimensions are a = 8.3693Å, b = 8.3693Å, c = 67.794 Å, V = 4112.5 Å3, close to those reported for the slag phase (Burns et al., 1998).
