Eucryptite

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Eucryptite
Eucryptite-pas-152b.jpg
Brownish grains of eucryptite embedded in albite from Branchville Quarry , Fairfield County, Connecticut ; ( Overall size of the sample: 9.3 × 7.0 × 2.8 cm)
General and classification
other names
  • Deep eucryptite
  • Lithium nepheline
chemical formula LiAl [SiO 4 ] (also α-LiAl [SiO 4 ])
Mineral class
(and possibly department)
Silicates and germanates - island silicates (nesosilicates)
System no. to Strunz
and to Dana
9.AA.05 ( 8th edition : VIII / A.01)
51.01.01.03
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol trigonal-rhombohedral; 3
Space group R 3 (No. 148)Template: room group / 148
Lattice parameters a  = 13.47  Å ; c  = 9.00 Å
Formula units Z  = 18
Frequent crystal faces {10 1 0}, {11 2 0}, {0001}
Physical Properties
Mohs hardness 6.5
Density (g / cm 3 ) measured: 2.657 to 2.666; calculated: 2.654 to 2.661
Cleavage according to {0001} and {10 1 0}
Break ; Tenacity clamshell; brittle
colour colorless, white, pink, brownish
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.570 to 1.573
n ε  = 1.583 to 1.587
Birefringence δ = 0.013
Optical character uniaxial positive
Other properties
Special features pink to red or orange fluorescence with short-wave UV light

Eucryptite is a rarely occurring mineral from the mineral class of "silicates and germanates". It crystallizes in the trigonal crystal system with the chemical composition LiAl [SiO 4 ], that is a lithium - aluminum - silicate that is structurally to the island silicates part (nesosilicates).

Eucryptite usually occurs in the form of fine-grained or coarse-grained to massive mineral aggregates , but rarely forms idiomorphic crystals of up to three centimeters in size, the surfaces of which have a glass-like sheen . In its pure form, eucryptite is colorless and transparent. Due to the multiple refraction of light due to its mostly polycrystalline formation, however, it can also appear white and, due to foreign admixtures, take on a pink or brownish color, the transparency decreasing accordingly.

Etymology and history

Eucryptite was first discovered in the "Fillow" quarry near Branchville in Fairfield County , Connecticut, and described in 1880 by George J. Brush and Edward S. Dana, who named the mineral after the ancient Greek words εὐ [eu] for "good" or " beautiful ”and κρυπτός [kryptós] for“ hidden ”or“ secret ”. The name refers to the fact that eucryptite is usually intimately fused with albite and is therefore difficult to analyze.

The type material of the mineral is stored at Yale University in New Haven (Connecticut) in the USA and the collection numbers 2.4206 , 2.4208 and 2.4209 .

classification

Already in the now outdated 8th edition of the mineral classification according to Strunz , the eucryptite belonged to the department of "island silicates (nesosilicates)", where together with phenakite and willemite as well as in the appendix Liberit the "phenakite series" with the system no. VIII / A.01 .

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. VIII / A.01-30 . In the “Lapis system” this corresponds to the more precise section “Island silicates with [SiO 4 ] groups”, where eucryptite, together with phenakite and willemite, also forms an independent, but unnamed group.

The 9th edition of Strunz's mineral systematics, valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, also classifies eucryptite in the category of "island silicates (nesosilicates)". However, this is further subdivided according to the possible presence of additional anions and the coordination of the cations involved , so that the mineral is classified according to its composition in the subsection “Island silicates without additional anions; Cations in tetrahedral [4] he coordination ”can be found, where together with phenakite, willemite and xingsaoite the“ phenakite group ”with the system no. 9.AA.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking area , also classifies eucryptite in the “island silicate minerals ” division. Here he is in the " phenakite group " with the system no. 51.01.01 can be found in the subsection “ Island silicates: SiO 4 groups only with cations in [4] coordination”.

Crystal structure

Eucryptite crystallizes trigonal in the space group R 3 (space group no. 148) with the lattice parameters a  = 13.47  Å and c  = 9.00 Å as well as 18 formula units per unit cell . Template: room group / 148

properties

Under short-wave UV light , some eucryptites show pink to red or orange fluorescence .

Modifications and varieties

The compound LiAl [SiO 4 ] is dimorphic . In addition to the trigonal modification, also known as α-eucryptite or deep eucryptite, there is a high-temperature modification called β-eucryptite, which crystallizes in hexagonal symmetry . β-eucryptite has a negative thermal expansion coefficient , high chemical and thermal stability and good lithium ion conductivity .

Education and Locations

Pink-colored, coarse eucryptite aggregate from the "Harding Mine", Picuris Pueblo , Taos County , New Mexico, USA (size: 4.0 × 2.0 cm)

Eucryptite forms in lithium-rich granitic pegmatites , where it is mostly found in weathered spodumene . However, it can also arise primarily and form masses up to 30 centimeters in size. Other accompanying minerals include albite , amblygonite , lepidolite , petalite and quartz .

As a rare mineral formation, eucryptite could only be detected at a few sites, whereby so far (as of 2013) around 30 sites are known. In addition to its type locality , the "Fillow" quarry near Branchville, the mineral occurred in the United States at White Picacho and the "Independence Mine" in Yavapai County of Arizona, at Collins Hill near Portland in Middlesex County of Connecticut, on Parker Mountain in Strafford County of New Hampshire, in the "Harding Mine" at Picuris Pueblo in Taos County of New Mexico, at Hiddenite and Kings Mountain in Alexander Counties of North Carolina and in the "Etta Mine" at Keystone in Pennington County of South Dakota.

Other locations include Egypt, Australia, China, Finland, Canada, Namibia, Portugal, Russia, Sweden, Zimbabwe, Spain and South Africa.

use

Eucryptite in the modification β-eucryptite is due to its special physical properties an important component of glass ceramics such as ceramic - hob and of superionic conductors .

See also

literature

  • GJ Brush, ES Dana: On the mineral locality at Branchville, Connecticut: Fourth paper . In: American Journal of Science . tape 120 , 1880, pp. 258–285 ( rruff.info [PDF; 2.6 MB ; accessed on November 4, 2019]).
  • KF Hesse: Crystal structures of natural and synthetic α-eucryptite, LiAlSiO4 . In: Journal of Crystallography . tape 172 , 1985, pp. 147–151 ( rruff.info [PDF; 693 kB ; accessed on November 4, 2019]).
  • Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 551 .

Web links

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

Individual evidence

  1. a b Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  662 (first edition: 1891).
  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.  535 (English).
  3. David Barthelmy: Eucryptite Mineral Data. In: webmineral.com. Accessed November 4, 2019 .
  4. a b c d Eucryptite . 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; 63  kB ; accessed on November 4, 2019]).
  5. a b c Eucryptite. In: mindat.org. Hudson Institute of Mineralogy, accessed November 4, 2019 .
  6. Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  7. Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed November 4, 2019 .
  8. ^ Natalia Dietrich: Manufacture and characterization of β-eucryptite and modified eucryptite ceramics LiAl1-yMySiO4 (M = Cr, Mn, Fe) for use as high-performance materials . 2007, p. 9 , doi : 10.22028 / D291-22444 ( available online at Saarland University [accessed November 4, 2019] dissertation under Prof. Horst Philipp Beck).
  9. Localities for Eucryptite. In: mindat.org. Hudson Institute of Mineralogy, accessed November 4, 2019 .
  10. Find location list for eucryptite in the Mineralienatlas and Mindat , accessed on November 4, 2019.
  11. ^ RO Jones, J. Harris: Mechanical & thermomechanical properties of materials. In: fz-juelich.de. Forschungszentrum Jülich , January 11, 2011, accessed on November 4, 2019 .