Beryllonite
| Beryllonite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | NaBe [PO 4 ] |
|
Mineral class (and possibly department) |
Phosphates, arsenates and vanadates |
|
System no. to Strunz and to Dana |
8.AA.10 ( 8th edition : VII / A.01) 01/38/12/01 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Room group (no.) | P 2 1 / n (No. 14) |
| Lattice parameters |
a = 8.18 Å ; b = 7.82 Å; c = 14.11 Å β = 90.0 ° |
| Formula units | Z = 12 |
| Twinning | according to {101} contact and penetration twins, according to {110} and {100} polysynthetic and pseudo-hexagonal star-shaped twins |
| Physical Properties | |
| Mohs hardness | 5.5 to 6 |
| Density (g / cm 3 ) | measured: 2.77 to 2.84; calculated: 2.805 |
| Cleavage | perfect after {010}, good after {100} |
| Break ; Tenacity | clamshell; brittle |
| colour | colorless, white, yellowish |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass to diamond luster, pearlescent luster on split surfaces |
| Crystal optics | |
| Refractive indices |
n α = 1.552 n β = 1.558 n γ = 1.561 |
| Birefringence | δ = 0.009 |
| Optical character | biaxial negative |
| Axis angle | 2V = 68 ° (measured) |
Beryllonite is a rarely occurring mineral from the mineral class of "phosphates, arsenates and vanadates". It crystallizes in the monoclinic crystal system with the chemical composition hub [PO 4 ], so it is chemically seen a sodium - Beryllium - phosphate .
Beryllonite mostly develops tabular to short prismatic crystals and twins , but also occurs in the form of spherulitic, fibrous or granular to massive mineral aggregates . In its pure form, beryllonite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also appear white and take on a yellowish color due to foreign admixtures, with the transparency decreasing accordingly. Uninjured crystal surfaces have a glass-like to diamond-like sheen , whereas cleavage surfaces have a more mother-of-pearl shimmer .
With a Mohs hardness of 5.5 to 6, beryllonite is one of the medium-hard minerals that is slightly easier to scratch with a steel file than the reference mineral orthoclase (6) .
Etymology and history
Beryllonite was first discovered on McKean Mountain near Stoneham in Oxford County in the US state of Maine . The mineral was described in 1888 by Edward Salisbury Dana , who named it after its main component beryllium.
The type material of the mineral is kept at Yale University in New Haven (Connecticut) in the USA (Catalog No. 3.1946).
classification
Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , beryllonite belonged to the mineral class of " phosphates , arsenates and vanadates " and there to the division of "anhydrous phosphates [PO 4 ] 3− , without foreign anions ", where together with alarsite , berlinite , hurlbutite , lithiophosphate , nalipoite , olympite and rodolicoite the group with small cations (Li, Be, Al, Fe 3+ ) with the system no. VII / A.01 .
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 beryllonite to the “Phosphates, etc., without further anions , without H 2 O” section and there in the subdivision "With small cations (some also with larger cations)", where he is the only member of the unnamed group 8.AA.10 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns beryllonite to the class of "phosphates, arsenates and vanadates" and there in the department of "anhydrous phosphates etc.". Here he is to be found as the only member of the unnamed group January 38, 2005 within the sub-section “Anhydrous phosphates etc. A + B 2+ XO 4 ”.
Education and Locations
Beryllonite forms as a secondary mineral through hydrothermal processes in granitic and alkaline pegmatites . Depending on where it was found, it can be associated with many different minerals such as albite , apatite , beryl , columbite , elbaite , eosphorite , herderite , cassiterite , lepidolite , lithiophilite , morinite , orthoclase , petalite , pollucite , quartz , triplite and varrynenite .
As a rare mineral formation, beryllonite could only be detected at a few sites, whereby so far (as of 2014) around 40 sites are known. In addition to its type locality McKean Mountain, the mineral occurred at the "Mcallister" site and in the "Lord Hill" quarry near Stoneham . In the vicinity of Stoneham, the largest known crystals and twins with diameters of up to 15 centimeters have also been found, although crystals up to 25 centimeters in size are said to have been discovered. Furthermore, the mineral is known in the United States from other places in Oxford County of Maine and from various sites in the states of Nevada and New Hampshire .
Other previously known sites are in Afghanistan, Brazil, China, Finland, France, Canada, Pakistan, Portugal, Sweden, the Czech Republic and the United Kingdom (UK).
Crystal structure
Beryllonite crystallizes monoclinically in the space group P 2 1 / n (space group no. 14) with the lattice parameters a = 8.18 Å ; b = 7.82 Å; c = 14.11 Å and β = 90.0 ° as well as 12 formula units per unit cell .
The crystal structure of Beryllonit consists of three BeO 4 - and PO 4 - tetrahedra which are connected to a network of six-membered rings and parallel to the b-axis are stacked. Similar to layered silicates, the rings and layers are connected to one another via shared corners, with channels parallel to the b-axis in which the sodium ions are accommodated.
use
Beryllonite is too sensitive for commercial use as a gemstone due to its perfect cleavage and fragility , which means that it could easily be destroyed by the heat, impact and pressure loads required for soldering and barrel work. Because of its relatively low Mohs hardness, it is also not suitable as a ring or arm jewelery, as it would scratch quickly.
The mineral is therefore especially faceted for collectors and offered in various cut shapes . Also of interest are the fibrous varieties that show the coveted cat-eye effect in cabochon cut .
See also
literature
- Edward S. Dana : Preliminary notice of beryllonite, a new mineral. In: American Journal of Science. Volume 136 (1888), pp. 290-291 ( PDF 217.75 kB )
- Helmut Schrätze, Karl-Ludwig Weiner: Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 610-611 .
- 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. 206 .
- Cally Hall: Gemstones: more than 130 types from around the world . Dorling Kindersley, Starnberg 2006, ISBN 978-3-8310-0891-9 , pp. 118 (English: DK Handbooks: Gemstones . Translated by Eva Dempewolf, Nature Library).
Web links
- Mineral Atlas: Beryllonite (Wiki)
- Web mineral - beryllonite
- realgems.org - Beryllonite (with picture examples of cut beryllonite)
- Database-of-Raman-spectroscopy - Beryllonite
- American-Mineralogist-Crystal-Structure-Database - Beryllonite
Individual evidence
- ↑ a b c d e f 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. 425 .
- ↑ a b c d e Beryllonite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 64.2 kB )
- ↑ a b c Mindat - Beryllonite
- ↑ Mindat - Number of localities for beryllonite
- ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 155 ( Dörfler Natur ).
- ↑ Find location list for beryllonite in the Mineralienatlas and Mindat
- ^ Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 611 .
- ↑ Gem Etiquette - Beryllonite