Dawsonite
| Dawsonite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | NaAl [(OH) 2 | CO 3 ] |
|
Mineral class (and possibly department) |
Carbonates and nitrates (formerly carbonates, nitrates and borates) |
|
System no. to Strunz and to Dana |
5.BB.10 ( 8th edition : V / C.02) 16a.03.08.01 |
| Similar minerals | Aragonite, Narolite, Skolezite |
| Crystallographic Data | |
| Crystal system | rhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal; 2 / m 2 / m 2 / m |
| Room group (no.) | Imam (No. 74) |
| Lattice parameters | a = 6.76 Å ; b = 10.24 Å; c = 5.58 Å |
| Formula units | Z = 4 |
| Frequent crystal faces | Pinacoids {001} {010} {100}, prism {110}, dipyramid {111} |
| Physical Properties | |
| Mohs hardness | 3 |
| Density (g / cm 3 ) | measured: 2.436; calculated: 2.431 |
| Cleavage | completely after {110} |
| Break ; Tenacity | uneven |
| colour | colorless, white, rarely pink |
| Line color | White |
| transparency | transparent |
| shine | Glass gloss or silk gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.466 n β = 1.542 n γ = 1.596 |
| Birefringence | δ = 0.130 |
| Optical character | biaxial negative |
| Axis angle | 2V = 77 ° (measured); 76 ° (calculated) |
| Other properties | |
| Chemical behavior | very sensitive to citric acid, alkalis and ammonia |
Dawsonite is a rarely occurring mineral from the mineral class of " carbonates and nitrates " (formerly carbonates, nitrates and borates, see classification ). It crystallizes in the orthorhombic crystal system with the composition NaAl [(OH) 2 | CO 3 ], so from a chemical point of view it is a sodium - aluminum carbonate with additional hydroxide ions .
Dawsonite develops fine-needle to leafy crystals up to 3.5 centimeters in length, which are stretched along the c-axis. In general, these are arranged in rosette-shaped, radial-radial to tufted or fibrous aggregates .
In its pure form, Dawsonite is colorless, transparent and has a glass-like sheen on the crystal surfaces . However, due to multiple refraction of light due to its fine-needle to fibrous formation, it can also appear white, creating a billowing, shimmering sheen similar to that of silk and reducing the transparency accordingly. Dawsonites colored pink due to foreign admixtures of chrome are rather rare .
With a Mohs hardness of 3, Dawsonite is one of the medium-hard minerals that can be scratched with a copper coin.
Special properties
"Swelling in front of the soldering tube with an intense yellow coloration of the flame, but not meltable [...] In the flask only emits water and carbon dioxide when heated up strongly ; remains stable up to 140 ° C. "
As a carbonate, Dawsonite dissolves in very dilute hydrochloric acid (HCl), releasing carbon dioxide. It is also soluble in citric acid , ammonia and other alkalis . This can be used to distinguish it from similar-looking zeolites .
Etymology and history
Dawsonite was first described by Bernard J. Harrington in 1874. The mineral was discovered in a Feldspatgang , which under construction on the campus of McGill University in Montreal ( Canada was excavated). Harrington himself worked at this university and honored John William Dawson , the then director of the university , by naming the mineral .
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the dawsonite still belonged to the common mineral class of "carbonates, nitrates and borates" and there to the department of "anhydrous carbonates with foreign anions ", where it belongs together with barensite and tunisite the "Dawsonite group" named after him with the system no. V / C.02 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), assigns the Dawsonite to the newly defined class of "carbonates and nitrates" (the borates form a separate class here), but also in the department of “carbonates with additional anions; without H 2 O “. However, this is further subdivided according to the predominant cations in the compound (mostly metals), so that the mineral can be found according to its composition in the sub-section "With alkalis etc.", where it is the only member of the unnamed group 5.BB.10 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Dawsonite, like the old Strunz system, to the common class of “carbonates, nitrates and borates” and there to the category of “carbonates with hydroxyl or halogen”. Here he is the only member of the unnamed group 16a.03.08 within the subsection “ Carbonates with hydroxyl or halogen and the general formula (AB) 2 (XO) 3 Z q ”.
Education and Locations
(field of view: 3.3 × 1.9 mm)
Dawsonite is found on fractures of hydrothermally modified feldspar-rich rocks, in nepheline syenites, and sodium-rich sediments. Carbon dioxide (CO 2 ) is necessary for the formation of dawsonite . The accompanying minerals include albite , analcime , aragonite , calcite , dolomite , fluorite , halite , cryolite , pyrite and quartz .
As a rare mineral formation, Dawsonite has so far (as of 2012) only been proven at a few sites, with around 90 sites being known. In addition to its type locality McGill University in Montreal, the mineral occurred in Canada on the Gray River on Newfoundland , in the Princess Sodalite Quarry in Hastings County (Ontario), on Muskiki Lake in Saskatchewan and at a few other sites in the vicinity of Montreal and Montérégie .
In Austria the mineral has so far only been found at the thermal spring discovered in Bad Loipersdorf and in the "Karl-August" tunnel near Fohnsdorf in Styria .
The only site known to date in Switzerland is the Simplon Pass near Brig , where the mineral was discovered in the excavated material during the construction of the Simplon Tunnel .
Further sites are found in Albania , Algeria , Argentina , Australia , Belgium , Bolivia , China , Italy , Japan , Mexico , New Zealand , Russia , Slovakia , Tanzania , the Czech Republic , Hungary and the United States of America (USA).
Crystal structure
Dawsonite crystallizes orthorhombically in the space group Imam (space group no. 74) with the lattice parameters a = 6.76 Å ; b = 10.24 Å and c = 5.58 Å and 4 formula units per unit cell .
literature
- Bernard J. Harrington: "Notes on dawsonite, a new carbonate", in: "The Canadian Naturalist and Quarterly Journal of Science", Volume 7 (1874), pp. 305-309 ( PDF, 388.4 kB ).
- Rupert Hochleitner, Stefan Weiß: "Profile Dawsonite", in: "Lapis" Volume 36, No. 6, p. 11/12, Munich 2012.
Web links
- Mineral Atlas: Dawsonite (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 .
- ↑ Webmineral - Dawsonites
- ↑ a b c John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: "Dawsonite", in: "Handbook of Mineralogy, Mineralogical Society of America", 2001 ( PDF; 65.6 kB )
- ↑ a b c Mindat - Dawsonite
- ↑ C. Hintez, Handbuch der Mineralogie, Vol. I-3 A, p. 2806, 1930
- ↑ H. Kurzweil: "Dawsonite from the deep borehole Binderberg 1, Eastern Styria - another deposit", 1980, kept in the annals of the Natural History Museum in Vienna ( PDF )
- ↑ Mindat - localities for Dawsonite