Despujolsite
| Despujolsite | |
|---|---|
 |
|
| General and classification | |
| other names |
IMA 1967-039 |
| chemical formula |
|
|
Mineral class (and possibly department) |
Sulphates (selenates, tellurates, chromates, molybdates and tungstates) |
|
System no. to Strunz and to Dana |
7.DF.25 ( 8th edition : VI / D.11) 07/31/06/01 |
| Similar minerals | Jouravskite (shape), ettringite (color) |
| Crystallographic Data | |
| Crystal system | hexagonal |
| Crystal class ; symbol | ditrigonal-dipyramidal; 6 m 2 |
| Space group | P 6 2 c (No. 190) |
| Lattice parameters | a = 8.56 Å ; c = 10.76 Å |
| Formula units | Z = 2 |
| Frequent crystal faces | {10 1 0}, {10 1 2}, {0001} |
| Physical Properties | |
| Mohs hardness | 2.5 |
| Density (g / cm 3 ) | 2.46 (measured); 2.54 (calculated) |
| Cleavage | no |
| Break ; Tenacity | clamshell; brittle and fragile |
| colour | yellow green, lemon yellow, lime green |
| Line color | probably light yellow |
| transparency | translucent to translucent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n ω = 1.656 n ε = 1.682 |
| Birefringence | δ = 0.026 |
| Optical character | uniaxial positive |
| Pleochroism | weakly from ω = pale yellow to ε = yellow |
| Other properties | |
| Chemical behavior | Dissolve in HCl with development of chlorine, with dilute HNO 3 first turning brown and then turning black, no impact from cold acetic acid recognizable |
Despujolsite is a very rarely occurring mineral from the mineral class of " sulfates (and relatives, see classification)". It crystallizes in the hexagonal crystal system with the chemical formula Ca 3 Mn 4+ [(OH) 6 | (SO 4 ) 2 ] · 3H 2 O, so from a chemical point of view it is a water-containing calcium - manganese- sulfate with additional hydroxide ions .
Despujolsite forms up to almost 2 cm in size, idiomorphic , {10 1 0} prismatic or {0001} tabular crystals , which can come together to form larger aggregates . Depending on their size, they are yellow-green, lemon-yellow or lime-green. Despujolsit is a typical hydrothermally formed mineral which in ductal mineralization in the environment of manganese - ore deposits has been found.
Etymology and history
The mineral was first observed in manganese ore samples from Tachgagalt (Anti-Atlas, Morocco) in 1962 and recognized a short time later as a new mineral. After intensive investigations by a French team of mineralogists and crystallographers around the Abbé Christophe Gaudefroy , the new mineral was presented to the IMA, which recognized it as a new mineral on December 18, 1967 with 17 against one vote. The first description as despujolsite by Christophe Gaudefroy, M.-M. Granger, François Permingeat and J. Protas in the “Bulletin de la Societe française de Minéralogie et de Cristallographie”.
The authors named the mineral in honor of the mining engineer Pierre Despujols (1888–1981), the founder of the "Service de la carte géologique du Maroc" (Moroccan Geological Service).
For decades the no more than 0.5 mm large crystals from Tachgagalt remained the only well-crystallized representatives of this mineral in the world. That only changed in 2005/2006 when despujolsite crystals with the extraordinary size of almost 2 cm were found in N'Chwaning II in South Africa. The South African despujolsite crystals are now considered to be the best for this species in the world.
The type material for despujolsite (holotype) comes from a donation by François Permingeate and is kept in the collection des Mines ParisTech (formerly: École nationale supérieure des mines de Paris ) in Paris (catalog no. Unknown).
classification
Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , despujolsite belonged to the mineral class of "sulfates (including selenates , tellurates , chromates , molybdates and tungstates )" and there to the department of "anhydrous sulfates, with foreign anions " , where together with Fleischerit , Mallestigit and Schaurteit he created the Schaurteit group with system no. VI / D.11 formed.
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns despujolsite to the category of "sulfates (selenates, etc.) with additional anions, with H 2 O". However, this is further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in the sub-section "With large and medium-sized cations" , where, together with Fleischerite, Mallestigit and Schaurteit, the Fleischerite group with the system No. 7.DF.25 forms.
The systematics of minerals according to Dana , which is common in the English-speaking world , also assigns despujolsite to the class of “sulfates, chromates and molybdates” and there to the “hydrated sulfates with hydroxyl or halogen” class. Here he is together with Schaurteit, Fleischerit and Mallestigit in the despujolsite group with system no. 07/31/06 within the subdivision of " Water-containing sulphates with hydroxyl or halogen with (A + B 2+ ) 2 (XO 4 ) Z q • x (H 2 O) ".
Chemism
Despujolsite has (based on 11 oxygen atoms per formula) the measured composition Ca 3.44 (Mn 4+ 0.86 Fe 3+ 0.06 ) Σ = 0.92 (S 0.96 O 4 ) 2 (OH) 6 · 3H 2 O, which was idealized to Ca 3 Mn 4+ (SO 4 ) 2 (OH) 6 · 3H 2 O.
Despujolsite is the manganese-dominant analogue of the germanium-dominated Schauteit, Ca 3 Ge (SO 4 ) 2 (OH) 6 3H 2 O and the Ca-Mn-dominant analogue of the Pb-Ge-dominated fleischerite, Pb 3 Ge (SO 4 ) 2 ( OH) 6 · 3H 2 O. Genplesite is the tin- dominant analogue of the manganese -dominated despujolsite.
Crystal structure
Despujolsite crystallizes hexagonally in the space group P 6 2 c (space group no. 190) with the lattice parameters a = 8.56 Å and c = 10.76 Å and two formula units per unit cell .
In the crystal structure of the Despujolsits alternate Mn (OH) 6 - octahedron and three Ca (OH) 4 (H 2 O) 2 O 2 - polyhedra existing units in the direction of the c-axis [0001] and share OH edges so that [Ca 3 Mn 4+ (OH) 6 (H 2 O) 6 O 3 ] 2− chains are formed. These chains are - similar to ettringite - by common O and H 2 O determined with SO 4 - tetrahedra linked.
According to recent crystal structure analyzes, the structure of the depujolsite is characterized by layers of CaO 8 polyhedra, which are connected to one another by Mn (OH) 6 octahedra and SO 4 tetrahedron in the direction of [0001]. There are two hydrogen bonds that stabilize the structural set-up. The calcium atoms are 8-fold coordinated with 4 (OH) - ions, 2 H 2 O molecules and 2 O atoms.
Fleischerite and Schaurteit and possibly also mallestigite are isotypic or isostructural to despujolsite.
properties
morphology
At the type locality, despujolsite forms idiomorphic crystals up to 0.5 mm in size, which usually sit individually in small cavities between the Gaudefroyite prisms. Despite the tendency to form single crystals, the Despujolsite can come together to form aggregates up to 5 mm in size. The crystals are developed in a long prism according to the prism {10 1 0} and also show the surfaces of the base pinacoid and the pyramid {10 1 1}, as the crystal drawing on the right also illustrates. In the N'Chwaning II and N'Chwaning III deposits, despujolsite preferably forms thick-tabular, more rarely long prismatic crystals that are always smaller than 2 cm.
physical and chemical properties
The color of despujolsite is yellow-green, lemon-yellow or light to deep lime-green, depending on the size of its crystals. The color of the despujolsite crystals seems to be sensitive to the spectrum, as one and the same crystal appears moss green in halogen light, while it has a lighter apple green color in fluorescent light - which is also shown in the adjacent pictures. No line color is specified for despujolsite, but it should be light yellow-green shades. The surfaces of the translucent to transparent crystals have a strong glass-like sheen , which corresponds to the relatively high birefringence of the mineral. In the thin section the mineral shows yellow hues under the microscope and a weak pleochroism from ω = pale yellow to ε = yellow. In the case of crossed polars , slightly anomalous greenish interference colors of the first order can appear.
No cleavage was found in the despujolite crystals , but because of their brittleness they break in a similar way to quartz , with the fracture surfaces being shell-shaped. The mineral has a Mohs hardness of 2.5. Despujolsite is therefore one of the soft minerals that are slightly easier to scratch than the reference mineral calcite with a copper coin. The measured density for despujolsite is 2.46 g / cm³ and the calculated density is 2.54 g / cm³. The macroscopic differentiation of despujolsite and jouravskite from the type locality Tachgagalt is difficult, but color and luster offer differentiation possibilities. The yellow of the despujolsite crystals is purer, without the greenish or orange tones of the jouravskite, and despujolsite has a more vivid glass luster than jouravskite.
In hydrochloric acid (HCl) to Despujolsit dissolved with evolution of chlorine on. With dilute nitric acid (HNO 3 ) it first turns brown and then turns black. Cold acetic acid does not cause any noticeable reactions.
Education and Locations
Despujolsite is formed as a hydrothermal formation in corridors in the vicinity of manganese deposits. Typically, the mineral sits in the cavities between Gaudefroyite crystals (Tachgagalt), but always without calcite, while Jouravskite is almost always accompanied by this mineral. If the formation of despujolsite and jouravykite is assumed to be volcanic with the action of fumaroles on manganese ores, despujolsite can only be formed in CO 2 -free areas. This is mainly achieved where all the CO 2 had already been used up during the crystallization of Gaudefroyit . In addition, the milieu changed from reducing to oxidizing at the end of mineral formation, which also explains the change from trivalent manganese in gaudefroyite to tetravalent manganese in despujolsite. In the deposits of the Kalahari manganese ore fields, the mineral is found in the form of crystals grown on a red matrix , probably colored by hematite .
As of 2016, despujolsite could only be described as a very rare mineral formation from just under ten sites. The type locality is corridor # 2 of the Tachgagalt manganese ore deposit, which was worked between 1937 and 1960 and has long since been abandoned, in the Ouarzazate province , Drâa-Tafilalet region , Morocco . Much better specimens, but often only perfectly formed crystals or crystal fragments, came from the “N'Chwaning II Mine” near Kuruman , Kalahari manganese ore fields, Northern Cape Province , South Africa in 2005/2006 . At the end of 2010, more or less identical material was found in the neighboring “N'Chwaning III mine”, which was only started in 2006. Other locations where despujolsite has been identified are the Mn-Co “Bungonia” deposit near Argyle , New South Wales , Australia ; the Sb deposit of the "Llapa Llapa Mine", Tomás Frías Province , Potosí Department , Bolivia , the "Shopov Cave" in the Balkans (Stara Planina), Bulgaria ; the Cu-Pb-Zn ganger ore deposit of the “Ogoya Mine” near the city of Komatsu City, Ishikawa Prefecture , Chūbu Region , Honshū , Japan ; the "San Jacinto Mudpots" at the Telica volcano , Volcano, Departamento León , Nicaragua and the beryllium deposit "Apache Warm Springs" in Ojo Caliente No. 2 District, Socorro County , New Mexico , United States .
use
Despujolsite is only of interest to collectors due to its rarity.
See also
literature
- Despujolsite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 63 kB )
- Christophe Gaudefroy, M.-M. Granger, François Permingeat, J. Protas: La despujolsite, une nouvelle espèce minérale . In: Bulletin de la Societe française de Minéralogie et de Cristallographie . tape 91 , 1968, p. 43–50 ( rruff.info [PDF; 5.0 MB ]).
Web links
- Mineral Atlas: Despujolsite (Wiki)
- Webmineral - Despujolsite (English)
- Mindat - Despujolsite (English)
- RRUFF Database-of-Raman-spectroscopy - Despujolsite (English)
- American-Mineralogist-Crystal-Structure-Database - Despujolsite (English)
Individual evidence
- ↑ a b c d e f Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 407 .
- ↑ a b Despujolsite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 63 kB ; accessed on December 18, 2017]).
- ↑ a b c d e f g Christophe Gaudefroy, M.-M. Granger, François Permingeat, J. Protas: La despujolsite, une nouvelle espèce minérale . In: Bulletin de la Societe française de Minéralogie et de Cristallographie . tape 91 , 1968, p. 43–50 ( rruff.info [PDF; 5.0 MB ]).
- ↑ Catalog of Type Mineral Specimens - D. (PDF 50 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 29, 2019 .
- ↑ a b Madison C. Barkley, Hexiong Yang, Stanley H. Evans, Robert T. Downs, J. Marcus Origlieri: Redetermination of despujolsite, Ca 3 Mn 4+ (SO 4 ) 2 (OH) 6 · 3H 2 O . In: Acta Crystallographica . E67, 2011, p. i47 – i48 , doi : 10.1107 / S1600536811030911 ( rruff.info [PDF; 1.1 MB ]).
- ↑ RRUFF Database-of-Raman-spectroscopy - Chemical analysis for despujolsite
- ↑ Mindat - Despujolsite mineral description
- ↑ Hermann H. Otto: The crystal structure of Fleischerit, Pb 3 Ge [(OH) 6 | (SO 4 ) 2 ] · 3H 2 O, as well as crystal chemical investigations on isotypic compounds . In: New Yearbook for Mineralogy, Treatises . tape 123 , 1975, pp. 160-190 .
- ↑ a b Marcus J. Origlieri, Robert T. Downs: Schaurteite, Ca 3 Ge (SO 4 ) 2 (OH) 6 · 3H 2 O . In: Acta Crystallographica . E69, 2013, p. i6 and sup-1 to sup-7 , doi : 10.1107 / S1600536812050945 ( rruff.info [PDF; 681 kB ]).
- ^ A b Bruce Cairncross, Nicolas J. Beukes: The Kalahari Manganese Field: the adventure continues . 1st edition. Random House Struik, Cape Town 2013, ISBN 978-1-920572-88-4 , pp. 197 .
- ↑ Mindat - Number of localities for despujolsite
- ↑ a b List of locations for despujolsite in the Mineralienatlas and Mindat