Spodumene

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Spodumene
Spodumene-gem7-78a.jpg
Spodumene from the pegmatite field Darra-i-Pech, Nangarhar, Afghanistan
Size: 12 × 6 × 3 cm
General and classification
chemical formula LiAl [Si 2 O 6 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DA.30 ( 8th edition : VIII / F.01)
65.01.04.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / c (No. 15)Template: room group / 15
Lattice parameters a  = 9.46  Å ; b  = 8.39 Å; c  = 5.22 Å
β  = 110.2 °
Formula units Z  = 4
Frequent crystal faces {100}, {010} and {110}
Twinning mostly after {100}
Physical Properties
Mohs hardness 6.5 to 7
Density (g / cm 3 ) 3.03 to 3.23
Cleavage complete after {110}
clear separation according to (100) below ~ 87 °
Break ; Tenacity uneven to scalloped
colour colorless, gray-white, pink to purple, green
Line color White
transparency transparent to translucent
shine Glass luster, pearlescent luster on fractured surfaces
Crystal optics
Refractive indices n α  = 1.648 to 1.661
n β  = 1.655 to 1.670
n γ  = 1.662 to 1.679
Birefringence δ = 0.014 to 0.018
Optical character biaxial positive
Axis angle 2V = 54 to 69 °
Pleochroism strong
Other properties
Special features yellow, orange or pink fluorescence

The lithium - mineral spodumene is a rarely occurring chain silicate from the group of pyroxene . It crystallizes in the monoclinic crystal system with the chemical composition LiAl [Si 2 O 6 ] and usually develops short, flattened crystals that are clearly striped in the longitudinal direction. The size of the crystals often fluctuates between a few centimeters and decimeters , but at some sites it can also reach record sizes of several meters.

Etymology and history

Spodumene was first found in 1800 near Utö in the Swedish landscape of Södermanland and described by José Bonifácio de Andrade e Silva , who named the mineral after an ancient Greek word because of its "ash-colored" combustion residues when heated, namely σποδούμενος spodúmenos , which means "to" as the present participle Burning ashes; ashen "means. The emphasis of the word spodumene is therefore on the middle syllable , but according to Duden the final syllable is stressed.

classification

In the outdated but still in use 8th edition of the mineral classification according to Strunz , the spodumene belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)", where it together with aegirin , augit , esseneit , hedenbergit , Jadeit , Jervisit , Johannsenite , kanoite , clino-enstatite , Klinoferrosilit , Kosmochlor , Namansilit , Natalyit , omphacite , Petedunnit and pigeonite the "pyroxene group, subgroup clinopyroxene" with the system number. VIII / F.01 .

The systematics of minerals according to Dana , which is common in the English-speaking world , also assigns the spodumene to the division of chain and ribbon silicates, but due to its crystal structure there it is classified into the sub-division of chain silicates with simple, unbranched chains, W = 1 with chains P = 2, where he is the only member of the Li-Pyroxene group.

Crystal structure

Spodumene crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 9.474  Å ; b  = 8.390 Å; c  = 5.219 Å and β = 110.07 ° as well as four formula units per unit cell . Template: room group / 15

For a detailed structure description, see pyroxene group .

properties

Pure spodumene is colorless. However, it can also be greenish (hiddenite), white, gray and yellow (triphane) or pink to violet (kunzite) color and also be two-colored due to foreign admixtures. Its pleochroism is very pronounced, which means that when the crystal is viewed along the x-axis, it shows a purple to green color and along the z-axis it is colorless.

Occasionally, spodumene shows yellow, orange, or pink fluorescence under short- and long-wave ultraviolet radiation .

Modifications and varieties

So far known color varieties are

  • the hiddenite , in which admixtures of chrome or iron produce the greenish color.
  • the pink to purple kunzite , which gets its color from the addition of manganese . Pleochroism , where the color changes from deep pink to pale or light pink when viewed from different directions.
  • the colorless to yellowish triphane

Education and Locations

Giant crystals from the Etta Mine, Black Hills, USA
(a miner for comparison, center right)

Spodumene forms as a characteristic mineral in lithium-rich pegmatites or granites either igneously , whereby rather cloudy variants arise, or through hydrothermal processes in the pegmatite cavities, which produce the clear and high-quality gemstone variants. The mineral is mostly found in paragenesis with quartz , albite , petalite , eucryptite , lepidolite and beryl as well as ore minerals such as amblygonite , cassiterite and tantalite (Mn) .

So far, spodumene has been found at around 450 sites worldwide (as of 2010), including in Afghanistan , Argentina , Ethiopia , Australia , Bolivia , Brazil , China , Germany , Finland , France , Ireland , Italy , Japan , Canada , Kazakhstan , Korea , Madagascar , Mexico , Mozambique , Myanmar , Namibia , Nigeria , Norway , Austria , Pakistan , Poland , Portugal , Russia , Sweden , Serbia , Zimbabwe , Somalia , Spain , Sri Lanka , South Africa , Swaziland , the Czech Republic , the United Kingdom and in the USA .

Particularly noteworthy is the "Etta Mine" near Keystone in Pennington County (South Dakota) , where the largest crystals up to 14 meters in length and 66 tons in weight have been found. Kunzites up to 40 centimeters long were recovered from the pegmatites near Mawi in Laghman (Afghanistan). The “Pala Chief Mine” on Chief Mountain in California supplied kunzite up to 28 centimeters long, and hiddenites up to 25 centimeters long came from the mines at Resplendor in Minas Gerais (Brazil).

use

Spodumene is one of the most important lithium ores . In the glass and ceramics industry, it is used as an additive to raw products for the manufacture of, for example, glass ceramic hobs, fiberglass or sanitary ceramics.

As a gem

Kunzite (left) in octagonal and hiddenite (right) in antique cut
Hiddenite: 2 × rough stones and 1 × faceted

Known Gem -Varietäten are mainly Kunzite and Hiddenite, either faceted or Cabochonen sanded be. Depending on the color, kunzite can imitate a pink sapphire or topaz , the noble beryl morganite , but also the quartz varieties amethyst and rose quartz . When Hiddenite is confusion among other golden beryl (heliodor), Green Garnet Demantoid , the rather bright green diopside and rarely, the emerald , and even with chrysoberyl , as well spodumens with cat's eye effect were found.

However, due to their good cleavability, both varieties are very sensitive to pressure and heat stress, such as those created when setting and soldering pieces of jewelry . When grinding, due to pleochroistic effects, care must be taken that the main axis of the crystal is perpendicular to the main panel of the desired facet cut so that the penetrating light creates strong colors.

Heating to around 300 to 400 ° C or exposure to light for a longer period of time, especially through spot irradiation, can bleach the stones. Another danger is their sensitivity to hydrofluoric acid , which quickly etches the crystal surfaces and makes them matt.

See also

literature

  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 236 .
  • Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 130 .
  • Martin Okrusch, Siegfried Matthes: Mineralogy. An introduction to special mineralogy, petrology and geology . 7th fully revised and updated edition. Springer Verlag, Berlin et al. 2005, ISBN 3-540-23812-3 , pp. 96, 251 .

Web links

Commons : Spodumene  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c Spodumene . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 74  kB ; accessed on January 27, 2017]).
  2. ↑ a b c d Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  621 .
  3. ↑ a b c d e Spodumene at mindat.org (English)
  4. ↑ Find spot list for spodumene in the Mineralienatlas and Mindat
  5. ↑ Mineralienatlas: Mineral records