Cummingtonite
| Cummingtonite | |
|---|---|
 Image width 2.2 mm |
|
| General and classification | |
| chemical formula | (Mg, Fe 2+ ) 7 [OH | Si 4 O 11 ] 2 |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.DE.05 ( 8th edition : VIII / F.07) 66.01.01.02 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | C 2 / m (No. 12) or P 2 1 / m (No. 11) |
| Lattice parameters |
a = 9.450 Å ; b = 18.108 Å; c = 5.298 Å β = 102.42 ° |
| Formula units | Z = 2 |
| Twinning | single or multiple twins parallel {100} |
| Physical Properties | |
| Mohs hardness | 5 to 6 |
| Density (g / cm 3 ) | 3.1 to 3.6 |
| Cleavage | completely after {110} |
| colour | gray-white, dark green, brown |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.639 to 1.671 n β = 1.647 to 1.689 n γ = 1.664 to 1.708 |
| Birefringence | δ = 0.025 to 0.037 |
| Optical character | biaxial positive |
| Axis angle | 2V = 65 to 90 ° |
The mineral cummingtonite is a rather seldom occurring chain silicate from the group of amphiboles . It crystallizes in the monoclinic crystal system with the chemical composition (Mg, Fe 2+ ) 7 [OH | Si 4 O 11 ] 2 and develops transparent to translucent, columnar, leafy or fibrous crystals or fibrous mineral aggregates of gray-white, dark green or brown Colour.
Cummingtonite forms a perfect mixed series with grunerite .
Etymology and history
Cummingtonite was first discovered in 1824 near Cummington in Hampshire County (Massachusetts) in the USA and described by Dewey, who named the mineral after its type locality .
classification
In the old (8th edition) and new systematics of minerals (9th edition) according to Strunz , the cummingtonite is found in the department of chain and band silicates (inosilicates). The old system does not subdivide this division any further and only summarizes the members of the amphibole group, whereby the Cummingtonite is not assigned to any special amphibole group. The new system, on the other hand, further subdivides the chain and ribbon silicates and the cummingtonite of the new subdivision of “chain and ribbon silicates with 2-periodic double chains, Si 4 O 11 ; Amphibole family, clinoamphibole ”too.
In the systematics of minerals according to Dana , cummingtonite also belongs to the division of chain and ribbon silicates, but there due to its crystal structure it belongs to the subdivision of chain silicates with double, unbranched chains (W = 2) and there to group 1 of the monoclinic Mg-Fe- Mn-Li amphiboles .
Crystal structure
Cummingtonite crystallizes monoclinically prismatic in the space group C 2 / m (space group no. 12) or P 2 1 / m (no. 11) with the average lattice parameters a = 9.450 Å determined in several measurements ; b = 18.108 Å; c = 5.298 Å and β = 102.42 ° as well as two formula units per unit cell .
Education and Locations
Cummingtonite usually forms regionally in medium-grade, metamorphic rocks , characteristically in metamorphically transformed iron formations, but also as a late mineral phase in some gabbros and norites .
In addition to its type locality Cummington in the USA, Cummingtonite has so far been detected at around 230 sites worldwide (as of 2009), including in several regions of Australia ; in Austrian Carinthia ; Santa Cruz Department in Bolivia; in some regions of Brazil ; at Oursi in Burkina Faso; in some regions of China ; Finland ; Brittany and Occitania in France and Martinique in French ; at Tarkwa in Ghana; Kitaa in Greenland; England in Great Britain; on the Cuyuni in Guyana; India ; Indonesia ; Italy ; on Hokkaidō and Honshū in Japan; in several regions of Canada ; Madagascar ; New Zealand ; Norway; in several regions of Russia ; some regions in Sweden ; at the Verzasca in Switzerland; on St. Lucia ; in Bratislavský kraj and Košice in Slovakia ; South Africa ; South Korea ; Andalusia and Extremadura in Spain; Bohemia in the Czech Republic as well as in many regions of the USA .
Trivia
The mineral is particularly popular among experts because of its English name, Cummingtonite , as "cumming tonite" means roughly "to experience an orgasm tonight". This is particularly evident in the form of T-shirt labels ("If you get with me you will be (Mg, Fe 2+ ) 7 [OH | Si 4 O 11 ] 2 ").
See also
literature
- 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. 626 .
Web links
- Mineral Atlas: Cummingtonite (Wiki)
- Webmineral - Cummingtonite (English)
Individual evidence
- ↑ a b c d e f Cummingtonite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 78.2 kB )
- ↑ a b c American Mineralogist Crystal Structure Database - Cummingtonite (English, 1998)
- ↑ a b c d e Mindat - Cummingtonite (English)
- ↑ Stefan Weiß: The large Lapis mineral directory . 5th edition. Christian Weise Verlag, Munich 2008, ISBN 3-921656-17-6 .
- ↑ Webmineral - Minerals Arranged by the New Dana Classification, inosilicates
- ↑ List of locations for cummingtonite in the Mineralienatlas and Mindat