Montenegro
| Montenegro | |
|---|---|
| General and classification | |
| other names |
IMA2018-060 |
| chemical formula | Ca 3 Sb 5+ 2 (Fe 3+ 2 Fe 2+ ) O 12 |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
| Crystallographic Data | |
| Crystal system | cubic |
| Crystal class ; symbol | cubic hexakisoctahedral; 4 / m 3 2 / m |
| Space group | Ia 3 d (No. 230) |
| Lattice parameters | a = 12.6093 (2) (natural) Å |
| Formula units | Z = 8 |
| Physical Properties | |
| Mohs hardness | 6.5 - 7 |
| Density (g / cm 3 ) | calculated: 4.72 (1) |
| Cleavage | not observed |
| Break ; Tenacity | shell-like |
| colour | black |
| Line color | brownish black |
| transparency | opaque |
| shine | Diamond luster |
| magnetism | not magnetic |
| Crystal optics | |
| Refractive index | n = not determined |
| Birefringence | δ = not determined |
| Optical character | not determined |
| Axis angle | 2V = not determined |
The mineral Monteneveit is a very rare oxide from the upper group of the garnet with the idealized composition Ca 3 Sb 5+ 2 (Fe 3+ 2 Fe 2+ ) O 12 . It crystallizes in the cubic crystal system with the structure of garnet.
Montenegro forms black, rounded crystals with a diamond luster of a maximum size of 0.4 mm.
So far, Montenegro has only been proven in its type locality , metamorphic sulphide layers of the Schneeberg mine on the Schneeberg of the same name (South Tyrol) in the province of South Tyrol in Italy .
Etymology and history
The metamorphic sulphide deposits on the Schneeberg were probably already mined for copper in prehistoric times and the extraction of silver is historically documented from the early 13th century .
In the 19th century, a handpiece from this old mining area came to Sweden, possibly from the Bockleitner Halde. Hjalmar Sjögren acquired in 1897 for 15 gold marks a piece of "Schneebergit" an iron Oxycalcioroméit by the company Dr. F. Krantz. Rheinisches Mineralien-Kontor and in 1901 Sjögren's collection was donated to the Naturhistoriska riksmuseet .
During an investigation of minerals from the Roméit group from various locations, a new Ca-Sb-Fe oxide from the garnet group was discovered in this handpiece almost 120 years later. It was named after its origin, the Monteneve (snow mountain) in South Tyrol.
classification
The structural classification of the International Mineralogical Association (IMA) counts the Monteneveit to the garnet upper group, where it formally forms with henritermierite and holtstamite the henritermierite group with 8 positive charges on the tetrahedrally coordinated lattice position. Unlike these two tetragonal minerals, Montenegro is cubic and contains neither (OH) groups nor vacancies on the tetrahedral position.
The 9th edition of the Strunz'schen mineral systematics, valid since 2001, does not list the Monteneveit. Like yafsoanite, it would be classified in division C (metal: oxygen = 2: 3, 3: 5 and comparable), subdivision C. (with large and medium-sized cations) within the class of oxides.
Crystal structure
Monteneveit crystallizes with cubic symmetry in Ia 3 d (No. 230) with 8 formula units per unit cell . The natural mixed crystal from the type locality has the lattice parameter a = 12.536 Å.
The structure is that of garnet . Calcium (Ca 2+ ) occupies the dodecahedral X positions surrounded by 8 oxygen, antimony (Sb 5+ ) the octahedral Y position surrounded by 6 oxygen and the tetrahedral Z position surrounded by 4 oxygen is with iron in two different oxidation states ( Fe 3+ , Fe 2+ ) occupied.
Chemism
Monteneveit has the simplified composition Ca 3 Sb 5+ 2 (Fe 3+ 2 Fe 2+ ) O 12 and is the first natural garnet with a mixed occupation of the tetrahedral position with divalent and trivalent cations. The measured composition from the type locality is [X] (Ca 2.97 Mg 0.03 ) [Y] (Sb 5+ 1.73 Sn 4+ 0.10 Fe 3+ 0.17 ) [Z] (Fe 3+ 2.43 Fe 2+ 0.37 Zn 2+ 0.20 ). This composition can be used as a mixed crystal of 37 mol% Monteneveit with 10 mol% Dzhuluit
- [Y] Sb 5+ + [Z] Fe 2+ = [Y] Sn 4+ + [Z] Fe 3+ ( Dzhuluit ),
20 mol% of the Zn analog from Monteneveit (Ca 3 Sb 5+ 2 (Fe 3+ 2 Zn 2+ ) O 12 )
- [Z] Fe 2+ = [Z] Zn 2+
and 33 mol% of the hypothetical end link Ca 3 (Sb 5+ 1.5 Fe 3+ 0.5 ) Fe 3+ 3 O 12
- [Y] Sb 5+ + 2 [Z] Fe 2+ = [Y] Fe 3+ + 2 [Z] Fe 3+
be understood.
Education and Locations
So far, Montenegro has only been detected in its type locality, the Schneeberg deposit in the province of South Tyrol in Italy, and occurs here in metamorphic sulphide layers. It formed metamorphically, probably at temperatures around 800 ° C and 8-10 kbar pressure, together with oxycalcioroméit during the breakdown of tetrahedron - (Fe). Other accompanying minerals are magnetite , sphalerite , chalcopyrite and probably calcite . Anthophyllite , Gudmundit and Genplesit occur in the handpiece not in direct contact with Monteneveit.
See also
Web links
- Mineral Atlas: Montenegro (Wiki)
- Entry on Montenegro at mindat.org
Individual evidence
- ↑ a b c d e f g h i j k l m n o p q r s Andreas Karlsson, Dan Holtstam, Luca Bindi, Paola Bonazzi, Matthias Konrad-Schmolke: Adding complexity to the garnet supergroup: monteneveite, Ca3Sb5 + 2 ( Fe3 + 2Fe2 +) O12, a new mineral from the Montenevemine, Bolzano Province, Italy . In: European Journal of Mineralogy . tape 32 , 2020, p. 77-87 ( researchgate.net [PDF; 5.2 MB ; accessed on May 15, 2020]).
- ↑ V. Mair, F. Vavtar, H. Schölzhorn, D. Schölzhorn: The lead-zinc ore mining on snow mountain, South Tyrol . In: Communications from the Austrian Mineralogical Society . tape 153 , 2007, p. 145–180 ( uibk.ac.at [PDF; 5.4 MB ; accessed on May 18, 2020]).
- ↑ List of localities for Montenegro in the Mineralienatlas and Mindat , accessed on May 15, 2020.