Carletonite
| Carletonite | |
|---|---|
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| General and classification | |
| other names |
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| chemical formula |
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Mineral class (and possibly department) |
Silicates and germanates ( phyllosilicates ) |
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System no. to Strunz and to Dana |
9.EB.20 ( 8th edition : VIII / H.07) 72.03.01.04 |
| Crystallographic Data | |
| Crystal system | tetragonal |
| Crystal class ; symbol | ditetragonal-dipyramidal; 4 / m 2 / m 2 / m |
| Space group | P 4 / mbm (No. 127) |
| Lattice parameters | a = 13.178 Å ; c = 16.695 Å |
| Formula units | Z = 4 |
| Frequent crystal faces | {100}, {001}, {110} |
| Physical Properties | |
| Mohs hardness | 4 to 4.5 (on {001}) |
| Density (g / cm 3 ) | 2.45 (measured); 2,426 (calculated) |
| Cleavage | very perfect after {001}, good after {110} |
| Break ; Tenacity | clamshell; brittle |
| colour | pink or pale to dark blue, colorless in small leaflets, also white and pale purple, often zoned |
| Line color | White |
| transparency | translucent to transparent, outer areas of the crystals often opaque |
| shine | Glass to mother-of-pearl; dull and waxy after a long time in air |
| Crystal optics | |
| Refractive indices |
n ω = 1.521 n ε = 1.517 |
| Birefringence | δ = 0.004 |
| Optical character | uniaxial negative |
| Pleochroism | weak from O = very pale blue to E = very pale pink-brown (only blue variety) |
| Other properties | |
| Chemical behavior | decomposed by HCl with SiO 2 residue; attacked by HNO 3 with gelatinization; only slightly attacked by H 2 SO 4 |
Carletonite is a very rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the tetragonal crystal system with the chemical formula KNa 4 Ca 4 [(OH, F) | (CO 3 ) 4 | Si 8 O 18 ] · H 2 O, and is thus chemically seen a hydrous potassium - sodium - calcium - silicate with additional carbonate groups and hydroxide ions or fluoride ions , which structurally belong to the layered silicates (phyllosilicates). The constituents fluoride and hydroxide ions indicated in the round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other constituents of the mineral.
Carletonite forms {001} prismatic crystals up to 6 cm in size, which are either colorless or pink or light to dark blue hues and are usually zoned. There are also massive, coarse aggregates in marble. The mineral is in gabbro intrusive syenite-alkali complex of Mont Saint-Hilaire found and occurs in core thermoplastic metamorphic stressed host rocks sxenolithe from schists and intermediate limestones (now Horn Felse and silicified marbles ) within nepheline on. Accompanying minerals are mainly pectolite , albite , fluorapophyllite , calcite , fluorite , steacyite , narsarsukite , leukosphenite and magnesio-arfvedsonite .
Etymology and history
As early as 1967, a team of American-Canadian scientists led by the mineralogist and crystallographer Professor George Y. Chao had presented a description of the minerals of the nepheline syenite from Mont Saint-Hilaire, pointing to the existence of ten unidentified minerals at Mont Saint-Hilaire pointed out. Among them was one that was characterized by characteristic gradual color transitions from pink to pale blue. This phase was provisionally referred to as "Mineral UK # 15" ("Unknown Number 15").
Further investigation resulted in UK # 15 being filed with the International Mineralogical Association (IMA) and recognized as a new mineral in 1969. It was described in 1971 by George Y. Chao of Carleton University , Ottawa , Canada and named as carletonite after the university at which it was first recognized and studied.
Type material of the mineral is in the Canadian Museum of Nature in Ottawa (formerly: National Museum of Natural Sciences) (catalog no. CMNMC 37135, holotype, 10 g), as well as in the Geological Survey of Canada in Ottawa (catalog no. NMNCC 012157 ( Mesotype, matrix level).
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , carletonite belongs to the mineral class of "silicates and germanates" and there to the department of "phyllosilicates", where it is the sole representative of the unnamed group with system no . VIII / H.07 .
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 carletonite to the class of “silicates and germanates” and there to the “phyllosilicates” section. This department is, however, further subdivided according to the structure of the layers, so that the mineral can be found in the subdivision "Double networks with 4 and 6-membered rings" according to its structure, where the unnamed group with the system no . 9.EB.20 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the carletonite to the class of "silicates and germanates" and there in the department of "layered silicate minerals". Here it is together with fluorapophyllite (K), hydroxyapophyllite (K) and fluorapophyllite (Na) in the " apophyllite group (4- and 8-membered rings) " with the system no. 72.03.01 within the sub-section " Layered silicates: two-dimensional, unlimited layers with rings other than six-membered: 3-, 4-, or 5-membered rings and 8-membered rings ".
Chemism
Carletonite has (based on 8 (Si, Al) atoms per formula) the measured composition K 0.74 Na 3.56 (Ca 3.74 , Mg 0.03 ) Σ = 3.77 (Si 7.89 , Al 0.11 ) Σ = 8.00 O 18 (CO 3 ) 3.65 F 0.41 2.05H 2 O, resulting in KNa 4 Ca 4 Si 8 O 18 (CO 3 ) 4 (F, OH) · H 2 O was idealized.
Carletonite has a non-stoichiometric composition and has deficits in potassium, sodium, calcium, CO 2 and fluorine. The water content stated in the analysis in the type publication is significantly higher than the structural formula requires, even if it is assumed that part of the water is in the form of fluorine-substituting hydroxyl groups. This excess water probably sits on the empty positions of the CO 2 group and leads to the stabilization of the defective structure.
Crystal structure
Carletonite crystallizes in the tetragonal crystal system in the space group P 4 / mbm (space group no. 127) with the lattice parameters a = 13.178 Å and c = 16.695 Å as well as four formula units per unit cell .
The structure of the carletonite consists of an apophyllite-like silicate double layer with four and eight rings, which are arranged in the direction of [001] with a carbonate layer (C1) with the composition Na 3 CO 3 · □ H 2 O and two carbonate layers (C2) Composition NaCa 2 CO 3 (F, OH) 0.5 alternates. In each case two independent SiO 4 - tetrahedra are linked together via a common oxygen atom and thus form roller rings around the four-fold axis of symmetry of the Carletonits. In the figure-of-eight, the apical oxygen atoms in alternating tetrahedra point in opposite directions. Each figure-of-eight is connected laterally via rings of four with four adjoining rings of figures across the diagonal mirror planes , which leads to an infinite individual layer. Each of the apophyllite-like Si 4 O 10 individual layers is connected to a further individual layer across the horizontal mirror plane (at z = 0.5). Both individual layers share half of their oxygen atoms that are not linked within the individual layer and thus form a Si 8 O 18 double layer.
The double-layer structure of the carletonite explains the very perfect cleavage of the mineral according to {001}.
The Si 8 O 18 double layers in the carletonite are structurally between tetragonal Si 4 O 10 single layers such as e.g. B. in the tetragonal representatives of the apophyllite group or in the Gillespit and the framework structures of some zeolites such as harmotome or phillipsite. For this reason, features of both related structures can be found in the carletonite structure.
The water of crystallization and the CO 2 are expelled between 650 and 750 ° C, which corresponds to a strong endothermic reaction at 692 ° C. After the loss of H 2 O and CO 2 , the crystal structure of the carletonite breaks down completely.
properties
morphology
Carletonite forms crystalline masses embedded in marbles and - in cavities - also up to 6 cm large, sharp-edged, shaped crystals that sit as parallel stacked aggregates on a base of white to pale blue carletonite crystals. The average size of the crystals only varies between 2 and 10 mm. The supporting and costume-defining crystal form of the short to long prismatic crystals is the tetragonal prism II position {100}, which is always accompanied by the basic pinacoid {001}. In most cases, the tetragonal prism I position {110} and / or the tetragonal dipyramid II position {101} are added. Tetragonal dipyramids in different positions {201}, {102}, {111} and the tetragonal prism I position {130} were observed on other surface shapes (compare the crystal drawings opposite).
physical and chemical properties
The colors of the carletonite crystals vary over a wide range. In addition to colorless crystals, there are also those with white, pink, pale lilac or pale blue to cornflower blue to dark blue coloration. Color-zoned crystals with concentric zones around [001] are very characteristic. The core area of the crystals is colored blue, while the outer zones are white, bluish white or beige in color. The transitions are partly gradual, partly very sharp, sometimes also irregular. The opaque outer zone, which can be mechanically separated from the core, probably represents a second generation of carletonite; it often contains internal defects and inclusions. The core areas of the crystals (i.e. the blue variety) show a weak pleochroism from O = very pale blue to E = very pale pink-brown.
The streak color of the carletonite is always white. The surfaces of the translucent to transparent crystals, occasionally opaque in the edge area, have a glass-like to mother-of-pearl-like sheen or are silky glossy. After a long time in the air a waxy sheen should develop. Naturally etched crystal surfaces are matt.
Carletonite has a very perfect cleavage according to {001} and good cleavage according to {110}, but due to its brittleness it breaks like amblygonite , with the fracture surfaces being uneven. With a Mohs hardness of 4 to 4.5, carletonite is one of the medium-hard minerals that, like the reference minerals fluorite and apatite, can be scratched more or less easily with a pocket knife. The measured density for carletonite is 2.45 g / cm³, the calculated density for the mineral is 2.426 g / cm³.
Carletonite is attacked by hydrochloric acid with the formation of a SiO 2 residue. The mineral is easily decomposed by nitric acid , forming a gelatinous residue. Carletonite is only slightly attacked by sulfuric acid .
Education and Locations
As a very rare mineral formation, Carletonite could so far (as of 2016) only be described by its type locality . This is the world-famous quarry of the Poudrette Quarry (also Demix Quarry, Uni-Mix Quarry, Desourdy Quarry and Carrière Mont Saint-Hilaire) on Mont Saint-Hilaire , regional county municipality La Vallée-du-Richelieu , Montérégie , Québec , Canada . Carletonite has been recovered here several times after it was first found in the 1960s.
Carletonite occurs exclusively in an intrusive gabbro-syenite alkali complex. It is found there in the core areas of thermometamorphically stressed secondary rock xenolites (former slates with intermediate limestones), which today are either greenish-gray or gray horn rock or silicified marbles. In the first of the occurrences described in the type publication, carletonite appeared in quartz veins within greenish-gray horn rock and was accompanied by lemon-yellow narsarsukite, calcite, violet fluorite and a little anklite , molybdenite , leukosphenite, lorenzenite (ramsayite) and galena . In a second occurrence, the mineral was found inside a xenolite about 60 cm in diameter. Its outer area consisted of a dark gray horn rock with large accumulations of solid pink and white albite. Its inner zone was composed of coarse-grained pectolite, medium-grained magnesio-arfvedsonite, solid pink albite, fine-grained quartz, fluorapophyllite, purple fluorite and carletonite. The massive, pink-colored carletonite, which took up approx. 80% by volume of the core area, was accompanied by idiomorphic magnesio-arfvedsonite crystals, fluorapophyllite and acicular leifite . In a third occurrence, the outer zone of the xenolite consisted of a coarse-grained marble and the inner zone of almost pure, radial-fiber pectolite. This contained pale blue carletonite together with microcline , magnesio arfvedsonite and tiny fluorapophyllite crystals. In all three deposits, the carletonite was only found in rough or massive form.
The first significant discovery of pale blue carletonite crystals up to 5 cm in length on matrix steps occurred in the summer of 1983. Between 1983 and 1987, beautiful steps with clear blue crystals up to 1 cm long, lining cavities were found several times. In the years from 1987 to 1988, in addition to beautiful specimens, mainly sharp-edged single crystals with an unusual color intensity were recovered. These include water-clear, deep blue crystals up to 1.5 cm in length as well as sharp-edged, prismatic crystals up to 6 cm in length, which have a distinct color zone structure (pale to deep blue inside / pink to colorless to white in the edge zone).
use
Although the crystals of the carletonite are fragile and easily split, some small gemstones could be cut. For example, a 0.34 carat, dark blue emerald cut stone is reported. It was later pointed out that as a result of the pleochroism when grinding the carletonite, its optical axis must be oriented perpendicular to the board surface in order to achieve a good color yield - but this leads to relatively small stones. Even so, the largest faceted carletonite is known to be a 1.48 ct stone owned by Gilles Haineault .
See also
literature
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Enke , Stuttgart 1978, ISBN 3-432-82986-8 , pp. 766 (first edition: 1891).
- Carletonite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 48 kB )
Web links
- Mineral Atlas: Carletonite (Wiki)
- Web mineral - carletonite
- Mindat - carletonite
- RRUFF Database-of-Raman-spectroscopy - Carletonite
- American-Mineralogist-Crystal-Structure-Database - Carletonite
Individual evidence
- ^ A b Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 662 .
- ↑ a b c d e f g h i j k l m n o p George Y. Chao: Carletonite, KNa 4 Ca 4 Si 8 O 18 (CO 3 ) 4 (F, OH) 7H 2 O, a new mineral from Mount St. Hilaire, Quebec . In: The American Mineralogist . tape 56 , 1971, p. 1855–1866 ( rruff.info [PDF; 559 kB ]).
- ↑ a b c d Carletonite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 48 kB )
- ↑ a b c d Lázló Horváth: Mineral species discovered in Canada (The Canadian Mineralogist Special Publication 6) . 1st edition. Mineralogical Association of Canada , Ottawa 2003, ISBN 978-0-921294-40-5 , pp. 35 .
- ↑ a b c d e f g Lázló Horváth, Robert Gait: The mineralogy of Mont Saint-Hilaire . In: The Mineralogical Record . tape 21 , 1990, pp. 284-359 .
- ↑ George Y. Chao, Donald C. Harris, Arthur W. Hounslow, Joseph A. Mandarino, Guy Perrault: Minerals from the nepheline syenite, Mont St. Hilaire, Quebec . In: The Canadian Mineralogist . tape 9 , 1967, p. 109-123 .
- ↑ a b c George Y. Chao: The crystal structure of carletonite, KNa 4 Ca 4 Si 8 O 18 (CO 3 ) 4 (F, OH) 7H 2 O, a double-sheet silicate . In: The American Mineralogist . tape 57 , 1972, p. 765-778 ( rruff.info [PDF; 880 kB ]).
- ↑ a b c Lázló Horváth, Elsa Horváth-Pfenninger: The minerals of Mont Saint-Hilaire . In: Lapis . 25 (issue 7/8), 2000, pp. 23-61 .
- ↑ Mindat - Number of localities for carletonite
- ↑ Find location list for carletonite in the Mineralienatlas and Mindat
- ^ John I. Koivula, Robert C. Kammerling, Emmanuel Fritsch: Gem News . In: Gems & Gemmology . tape 28 , 1992, pp. 129-139 .