Danburite
| Danburite | |
|---|---|
 (size: 9.9 × 7.9 × 7.5 cm) |
|
| General and classification | |
| chemical formula | Ca [B 2 Si 2 O 8 ] |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.FA.65 ( 8th edition : VIII / J.08) 56.03.01.01 |
| Similar minerals | Calcite , dolomite , hambergite , phenakite , quartz and citrine , topaz |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal 2 / m 2 / m 2 / m |
| Room group (no.) | Pnam (No. 62) |
| Lattice parameters | a = 8.04 Å ; b = 8.75 Å; c = 7.73 Å |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 7 to 7.25 |
| Density (g / cm 3 ) | measured: 2.93 to 3.02; calculated: 2.99 |
| Cleavage | indistinct after {001} |
| Break ; Tenacity | uneven to slightly scalloped; brittle |
| colour | colorless, white, gray, greenish, reddish, yellowish, brownish |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass gloss to fat gloss, matt |
| Crystal optics | |
| Refractive indices |
n α = 1.627 to 1.633 n β = 1.630 to 1.636 n γ = 1.633 to 1.639 |
| Birefringence | δ = 0.006 |
| Optical character | alternating biaxially |
| Axis angle | 2V = measured: 88 to 90 °; calculated: 88 ° |
| Other properties | |
| Chemical behavior | Meltable in front of the soldering tube , melting ball jellied in hydrochloric acid |
Danburite is a mineral from the mineral class of " silicates and germanates ", which can sometimes be abundant in various locations, but is generally not very common. It crystallizes in the orthorhombic crystal system with the chemical composition Ca [B 2 Si 2 O 8 ] and develops mostly prismatic to columnar crystals up to 50 cm in length, but also granular or massive mineral aggregates .
Pure danburite is transparent and colorless. However, due to multiple refraction due to lattice construction defects or multicrystalline training, it can also appear white and, due to various foreign admixtures, take on a gray, green, reddish, yellowish or brownish color, whereby the transparency decreases accordingly. However, its line color is always white. Visible crystal surfaces have a glass-like to grease-like sheen , while massive aggregates are more matt.
With a Mohs hardness of 7 to 7.25, danburite is one of the hard minerals and, like the reference mineral quartz , is able to scratch window glass. Danburite shows only indistinct cleavage according to {001} and an uneven to slightly mussel-like, brittle fracture.
Etymology and history
Danburite was first discovered near Danbury in Fairfield County in the US state of Connecticut and described in 1839 by Charles Upham Shepard , who named the mineral after its type locality .
classification
In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Danburit belonged to the mineral class of "silicates and Germanates" and then to the Department of " framework silicates (tectosilicates)" where he collaborated with Reedmergnerit formed a separate group.
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 danburite to the class of “silicates and germanates”, but in the newly defined section of “tectosilicates” without zeolitic H 2 O “. This section is further subdivided according to the possible presence of further anions , so that the mineral can be found in the sub-section "Tectosilicates (tectosilicates) without additional anions" according to its composition, where the "Danburite group" with the system no. 9.FA.65 and the other members Maleevit and Pekovit .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns danburite to the class of "silicates and germanates", but there in the department of " group silicates : Si 2 O 7 groups and O, OH, F and H 2 O " a. Here he is also the namesake of the "Danburit group" with the system no. 56.03.01 within the subsection of the " Group silicates: Si 2 O 7 groups and O, OH, F and H 2 O with Si2O7 with borate groups ".
Crystal structure
Danburite crystallizes orthorhombically in the space group Pnam (space group no. 62) with the lattice parameters a = 8.04 Å ; b = 8.75 Å and c = 7.73 Å and 4 formula units per unit cell .
properties
In front of the soldering tube, danburite phosphoresces and slowly melts into a white, blistered, translucent glass. With borax , it melts into a translucent pearl with an effervescence. In a powdered state, danburite slowly decomposes into hydrochloric acid .
Education and Locations
Danburite is formed by hydrothermal processes in pegmatite cavities as well as in ore and alpinotype veins . But it can also arise metamorphically in skarns . Accompanying minerals include albite , anhydrite , apophyllite , axinite , bakerite , calcite , datolite , dolomite , fluorite , gypsum , grossular , quartz , stilbit , titanite as well as various mica and tourmalines .
In total, danburite has so far (as of 2011) been found at around 120 sites. In addition to its type locality Danbury in Connecticut, the mineral was also found in the USA in Clarke County in Alabama, near Port Clarence in Alaska, on Maude Hill in Cochise County in Arizona, near Iberville Parish in Louisiana, near Stratton in Texas, in San Juan County and gold Hill ( Tooele County ), on Green Mountain in King County in Washington and in several places in the US states California , Montana and New York .
In Germany, the mineral has so far been found near Hildfeld and Silbach in the Sauerland (North Rhine-Westphalia) and near Staßfurt in Saxony-Anhalt. In Austria, the mineral has so far been found in the Scheiblinggraben near Bad Gastein and in the Kötschachtal (part of the Gastein Valley ) and in Switzerland it was found in Val Cadlimo in the canton of Ticino , in the Etzlital in the canton of Uri and in several places in the canton of Graubünden .
Other locations include Afghanistan , Australia , Bolivia , China , France , Iran , Italy , Japan , Canada , Madagascar , Mexico , Myanmar , Namibia , Nepal , Norway , Romania , Russia , Slovakia , Tajikistan , Tanzania , Czech Republic , Turkmenistan , United Kingdom (Great Britain) and Vietnam .
use
Although danburite can look very similar to different gemstones such as phenakite , quartz (especially the citrine variety ) or topaz, depending on the color , and is also easy to grind due to its great hardness and low tendency to split , it is only occasionally called Gemstone used. Its great sensitivity to heat, such as B. arise when soldering jewelry with Danburites, would bring the stone to melt quickly. That makes it a difficult stone to handle.
See also
literature
- Charles Upham Shepard: The Danburite, a new mineral species (PDF; 108 kB), in: JC Poggendorf (ed.): Annalen der Physik und Chemie , Volume 50, Verlag Johann Ambrosius Barth, Berlin-Leipzig 1840, p. 182 (excerpt from Silliman's Journal, Volume XXV, p. 138)
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, Stuttgart 1978, ISBN 3-432-82986-8 , p. 783 .
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 267 ( Dörfler Natur ).
- Walter Schumann: Precious stones and gemstones. All species and varieties in the world. 1600 unique pieces . 13th revised and expanded edition. BLV Verlags-GmbH., Munich et al. 2002, ISBN 3-405-16332-3 , p. 198 .
- CU Shepard (1839): AMERICAN JOURNAL OF SCIENCE AND ARTS 35, 137
- MW Phillips, GV Gibbs, PH Ribbe (1974): The crystal structure of Danburite: A comparison with Anorthite, Albite, and Reedmergnerite , AMERICAN MINERALOGIST 59, 1-2, 79-85
Web links
- Mineral Atlas: Danburite (Wiki)
- realgems.org - Danburite (with photos of Danburite in different cuts)
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. 697 .
- ↑ Webmineral - Danburite (English)
- ↑ a b Handbook of Mineralogy - Danburite (English, PDF 73.5 kB)
- ↑ a b c d Danburite at mindat.org (engl.)
- ↑ Mindat - number of known sites
- ^ Precious stone etiquette by Prof. Leopold Rössler - Danburit