| Haüyne | |
|---|---|
 Hauyne fromMayen, Eifel Mts,Rhineland-Palatinate, Germany | |
| General | |
| Category | Tectosilicateminerals,feldspathoidgroup,sodalite group |
| Formula | Na3Ca(Si3Al3)O12(SO4)[1] |
| IMA symbol | Hyn[2] |
| Strunz classification | 9.FB.10 (10 ed) 8/J.11-30 (8 ed) |
| Dana classification | 76.2.3.3 |
| Crystal system | Isometric |
| Crystal class | Hextetrahedral (43m) H-M symbol (4 3m) |
| Space group | P43n |
| Unit cell | a = 9.08 – 9.13 Å; Z = 2 |
| Identification | |
| Formula mass | 1,032.43 g/mol[3] |
| Color | Blue, white, gray, yellow, green, pink |
| Crystal habit | Dodecahedral or pseudo-octahedral |
| Twinning | Common on {111} |
| Cleavage | Distinct on {110} |
| Fracture | Uneven to conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5 to 6 |
| Luster | Vitreous to greasy |
| Streak | Very pale blue to white |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.4 to 2.5 |
| Optical properties | Isotropic |
| Refractive index | n = 1.494 to 1.509 |
| Birefringence | None, isotropic |
| Pleochroism | None, isotropic |
| Fusibility | 4.5[4] |
| Solubility | Gelatinises in acids |
| Other characteristics | May fluoresce orange to pink under longwaveultraviolet light[5][6] |
| References | [3][4][5][6] |
Hauyne orhaüyne, also calledhauynite orhaüynite (/ɑːˈwiːnaɪt/ah-WEE-nyte),[7] old nameAzure spar,[8]: 571 is a raretectosilicatesulfate mineral withendmember formulaNa3Ca(Si3Al3)O12(SO4).[1] As much as 5wt %K2O may be present, and alsoH2O andCl. It is afeldspathoid and a member of thesodalite group.[4][5] Hauyne was first described in 1807 from samples discovered in Vesuvian lavas inMonte Somma, Italy,[9] and was named in 1807 by Brunn-Neergard for the French crystallographerRené Just Haüy (1743–1822).[4] It is sometimes used as a gemstone.[10]
Formulae:[1]
All these minerals arefeldspathoids.Haüyne forms asolid solution with nosean and with sodalite. Complete solid solution exists between synthetic nosean and haüyne at 600 °C, but only limited solid solution occurs in the sodalite-nosean and sodalite-haüyne systems.[11]
The characteristic blue color of sodalite-group minerals arises mainly from cagedS−3 andS4 clusters.[12]
Haüyne belongs to the hexatetrahedralclass of theisometric system,43m,space group P43n. It has one formula unit perunit cell (Z = 1), which is acube with side length of 9Å. More accurate measurements are as follows:
Allsilicates have a basic structural unit that is atetrahedron with anoxygenion O at each apex, and asilicon ion Si in the middle, forming (SiO4)4−. Intectosilicates (framework silicates) each oxygen ion is shared between two tetrahedra, linking all the tetrahedra together to form a framework. Since each O is shared between two tetrahedra only half of it "belongs" to the Si ion in either tetrahedron, and if no other components are present then the formula is SiO2, as inquartz.
Aluminium ions Al, can substitute for some of the silicon ions, forming (AlO4)5− tetrahedra. If the substitution is random the ions are said to be disordered, but in haüyne the Al and Si in the tetrahedral framework are fully ordered.[4]
Si has a charge 4+, but the charge on Al is only 3+. If all thecations (positive ions) are Si then the positive charges on the Si's exactly balance the negative charges on the O's. When Al replaces Si there is a deficiency of positive charge, and this is made up by extra positively charged ions (cations) entering the structure, somewhere in between the tetrahedra.
In haüyne these extra cations aresodium Na+ andcalcium Ca2+, and in addition the negatively chargedsulfate group (SO4)2− is also present. In the haüyne structure the tetrahedra are linked to form six-membered rings that are stacked up in an ..ABCABC.. sequence along one direction, and rings of four tetrahedra are stacked up parallel to another direction. The resulting arrangement forms continuous channels that can accommodate a large variety ofcations andanions.[11]
Haüyne crystallizes in theisometric system forming raredodecahedral or pseudo-octahedral crystals that may reach 3 cm across; it also occurs as rounded grains. The crystals are transparent to translucent, with a vitreous to greasyluster. The color is usually bright blue, but it can also be white, grey, yellow, green and pink.[4][5][6] Inthin section the crystals are colorless or pale blue,[6][13] and thestreak is very pale blue to white.
Haüyne isisotropic. Truly isotropic minerals have nobirefringence, but haüyne is weakly birefringent when it containsinclusions.[6][13] Therefractive index is 1.50; although this is quite low, similar to that of ordinary window glass, it is the largest value for minerals of the sodalite group.[13] It may show reddish orange to purplish pinkfluorescence under longwaveultraviolet light.[5][6]
Cleavage is distinct to perfect, andtwinning is common, as contact, penetration and polysynthetic twins.[4] The fracture is uneven toconchoidal, the mineral isbrittle, and it hashardness5+1⁄2 to 6, almost as hard asfeldspar. All the members of the sodalite group have quite low densities, less than that ofquartz; haüyne is the densest of them all, but still itsspecific gravity is only 2.44 to 2.50.[13] If haüyne is placed on a glass slide and treated withnitric acid HNO3, and then the solution is allowed to evaporate slowly,monoclinic needles ofgypsum form. This distinguishes haüyne fromsodalite, which forms cubic crystals ofchlorite under the same conditions.[13] The mineral is notradioactive.[3]
Haüyne occurs inphonolites and relatedleucite- ornepheline-rich,silica-poor,igneous rocks; less commonly in nepheline-freeextrusives[3][4][5][6] andmetamorphic rocks (marble).[4] Associated minerals includenepheline,leucite,titanianandradite,melilite,augite,sanidine,biotite,phlogopite andapatite.[6]
Thetype locality isLake Nemi,Alban Hills, Rome Province, Latium, Italy.[5]
Occurrences include:
