Cavansite
| Cavansite | |
|---|---|
_2.JPG) |
|
| General and classification | |
| other names |
IMA 1967-019 |
| chemical formula | Ca [V 4+ O | Si 4 O 10 ] • 4H 2 O |
|
Mineral class (and possibly department) |
Silicates and germanates - layered silicates (phyllosilicates) |
|
System no. to Strunz and to Dana |
9.EA.50 ( 8th edition : VIII / H.36) 03/07/01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal 2 / m 2 / m 2 / m |
| Room group (no.) | Pcmn (No. 62) |
| Lattice parameters | a = 9.79 Å ; b = 13.64 Å; c = 9.63 Å |
| Formula units | Z = 4 |
| Frequent crystal faces | {110}, {101} |
| Physical Properties | |
| Mohs hardness | 3 to 4 |
| Density (g / cm 3 ) | 2.21 to 2.31; calculated: 2.33 |
| Cleavage | good after {010} |
| Break ; Tenacity | uneven; brittle |
| colour | green-blue to blue |
| Line color | Light Blue |
| transparency | transparent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.542 (2) n β = 1.544 (2) n γ = 1.551 (2) |
| Birefringence | δ = 0.009 |
| Optical character | biaxial positive |
| Axis angle | 2V = 52 ° (measured); 58 ° (calculated) |
Cavansite is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the orthorhombic crystal system with the chemical composition Ca [V 4+ O | Si 4 O 10 ] · 4H 2 O, so it is a calcium - vanadium - sheet silicate .
Cavansite is transparent and develops long, prismatic to needle-like crystals , but also radial mineral aggregates of blue to greenish-blue color with glass gloss on the surfaces.
Etymology and history
The name Cavansit is an artificial word, consisting of the abbreviations of the main elements calcium (Ca), vanadium (V, van) and silicon (Si) contained in the mineral and the appended 't' after the Greek word lithos for stone.
Cavansite was first discovered in the fall of 1960 by Mr and Mrs Leslie Perrigo. They found a blue mineral on a large rock wall near the Owyhee Dam in Oregon and, together with Mr. and Mrs. Frank Zimmerman, collected some samples and gave them to Dr. Paul Desautels of the United States National Museum, who realized that it could possibly be a new mineral.
Three years later, amateur mineralogist and collector John Cowles (1907–1985) discovered a similar looking blue mineral in the Charles W. Chapman quarry near Goble about 350 miles northwest of the Owyhee Dam and showed it to Lloyd W. Staples with the request, identify the mineral. Staples analyzed it with Howard T. Evans (Jr.) and James R. Lindsay and, on the one hand, realized that it was identical to the material from the Owyhee Dam and a previously unknown type of mineral. During the crystallographic analysis of a sample from the Owyhee Dam, a few crystal twins were found that were similar to cavansite in appearance and physical properties and also had the same chemical composition. The crystals differed from Cavansite in the structure of the silicate layers. Staples, Evans and Lindsay named this new mineral pentagonite in reference to its characteristic, pentagonal crystal twins.
Since the mineral was not named after Cowles due to unfortunate circumstances, the mineral cowlesite was later named after him as compensation .
classification
Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , cavansite belonged to the mineral class of "silicates and germanates" and there to the department of "phyllosilicates", where together with pentagonite it belongs to the unnamed group VIII / H .36 made.
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 cavansite to the class of "silicates and germanates" and there in the department of "phyllosilicates". This section is, however, further subdivided according to the structure of the layers, so that the mineral can be found according to its structure in the sub-section "Simple tetrahedral networks with 4, 5, (6) and 8 participating rings", where it is the only member of the unnamed group 9.EA.50 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns cavansite to the class of "silicates and Germanates", but there it is in the more finely subdivided division of "layered silicates: modulated layers". Here it is together with pentagonite in the group of "vanadium layered silicates" with the system no. 74.03.07 within the sub-section " Layered Silicates: Modulated Layers with Connected Strips ".
Modifications and varieties
The compound Ca [V 4+ O | Si 4 O 10 ] · 4H 2 O is dimorphic and occurs in nature in addition to the orthorhombically crystallizing cavansite also as orthorhombic pentagonite , but in a different space group crystallizing pentagonite .
Education and Locations
Cavansite is mainly formed hydrothermally in cavities in volcanic rocks such as basalt and tuff . The accompanying minerals include analcime , apophyllite , calcite , chalcosine , heulandite , solid copper , mordenite , pentagonite, stilbitite and thomsonite .
As a rare mineral formation, cavansite has only been found at a few sites so far, although 13 sites are known to date (as of 2012).
The zeolite quarries in the Pune district (formerly anglicizing Poona (h) ) in the Indian state of Maharashtra, where radial aggregates of up to three centimeters in diameter were found, are known due to the extraordinary cavansite finds.
In addition to its type locality Owyhee Dam and the only other known location Goble in the US state of Oregon, the mineral also appeared in the Municipal quarry near Morro Reuter in Brazil and near Aranga in the Kaipara District in New Zealand.
Crystal structure
Cavansite crystallizes orthorhombically in the space group Pcmn (space group no. 62) with the lattice parameters a = 9.79 Å ; b = 13.64 Å and c = 9.63 Å and 4 formula units per unit cell .
use
Cavansit has no technical or economic significance. It is only popular among collectors because of its brilliant blue sheen.
See also
literature
- Lloyd W. Staples, Howard T. Evans (Jr.), James R. Lindsay: Cavansite and pentagonite, new dimorphous calcium vanadium silicate minerals from Oregon , in: American Mineralogist , Volume 58 (1973), pp. 405-411 ( PDF 760 kB )
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, Stuttgart 1978, ISBN 3-432-82986-8 , p. 765 .
Web links
- Mineral Atlas: Cavansite (Wiki)
Individual evidence
- ↑ a b c d e 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. 661 .
- ↑ Webmineral - Cavansite
- ↑ a b c d e John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Cavansite , in: Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 73 kB )
- ↑ a b c d Mindat - Cavansite
- ↑ Mineral Atlas: Cowlesite (Wiki)
- ↑ Mindat - Number of localities for Cavansite
- ^ Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 260 .