Pectolite

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Pectolite
Pectolite-112882.jpg
Pectolite from Bergen Hill, New Jersey, USA
General and classification
chemical formula Ca 2 Na [Si 3 O 8 OH]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DG.05 ( 8th edition : VIII / F.18)
65.02.01.04
Similar minerals Wollastonite , bustamite
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 7.98  Å ; b  = 7.02 Å; c  = 7.02 Å,
α  = 90.5 °; β  = 95.1 °; γ  = 102.5 °
Formula units Z  = 2
Twinning rare, twin axis [010], intergrowth plane {100}
Physical Properties
Mohs hardness 4.5 to 5
Density (g / cm 3 ) measured: 2.84 to 2.90; calculated: 2.87
Cleavage completely according to {100} and {001}
Break ; Tenacity uneven; brittle
colour colorless, white, gray-white, yellowish, pink, sea blue (Larimar)
Line color White
transparency translucent to opaque
shine weak glass gloss, silk gloss
Crystal optics
Refractive indices n α  = 1.594 to 1.610
n β  = 1.603 to 1.614
n γ  = 1.631 to 1.642
Birefringence δ = 0.037
Optical character biaxial positive
Axis angle 2V = measured: 50 to 63 °; calculated: 42 to 60 °
Pleochroism not known
Other properties
Special features Triboluminescence

Pectolite , sometimes also written as pectolite (h) or peckolite or known under the synonymous names gonsogolite , stellite and Alaska jade , is a rather seldom occurring mineral from the mineral class of "silicates and germanates" with the chemical composition Ca 2 Na [Si 3 O 8 OH] and is therefore chemically a basic calcium - sodium silicate. Structurally, pectolite belongs to the chain and band silicates .

Pectolite crystallizes in the triclinic crystal system with the chemical composition and often develops fibrous to columnar crystals in a parallel or radial arrangement.

Is known mainly as a gemstone used, blue white clouded over variety Larimar .

Etymology and history

Pectolite was first described in 1828 by Franz von Kobell , who found the mineral near Sano, a district of the Italian municipality of Mori in the province of Trento (Trentino-Alto Adige region), on the northeastern foothills of Monte Altissimo di Nago , which belongs to Monte Baldo . He named it after the ancient Greek words πηκτός pektos for “curdled” or “made from different parts” and λίθος lithos for stone.

classification

Already in the outdated, but still in use 8th edition of the mineral systematics according to Strunz , the pectolite belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)", where together with bustamite, cascandite , denisovite , Ferrobustamit , Foshagit , Jennit , Serandit , Tanohatait , Vistepit and wollastonite the "wollastonite group" with the system no. VIII / F.18 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the IMA, also classifies pectolite as a division of "chain and band silicates". However, this is further subdivided according to the structure of the chain formation, so that the mineral can be found according to its structure in the sub-section "Chain and band silicates with 3-periodic single and multiple chains", where it is found together with bustamite, ferrobustamite, sérandite, tanohataite and wollastonite the “wollastonite group” with the system no. 9.DG.05 forms.

The systematics of minerals according to Dana also assigns the pectolite to the class of "silicates and germanates" and there in the department of "chain silicate minerals". Here it is also in the "wollastonite group" with the system no. 65.02.01 to be found in the subsection " Chain Silicates: Simple unbranched chains, W = 1 with chains P = 3 ".

Crystal structure

Pectolite crystallizes triclinic in the space group P 1 (space group no. 2) with the lattice parameters a  = 7.98  Å ; b  = 7.02 Å; c  = 7.02 Å; α  = 90.5 °; β  = 95.1 ° and γ  = 102.5 ° as well as 2 formula units per unit cell . Template: room group / 2

properties

Water-clear, transparent pectolite from the Poudrette pit, Mont Saint-Hilaire, Rouville, Montérégie, Québec, Canada

Pure pectolite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also appear white and, due to foreign admixtures, take on a gray-white, yellowish, pink or, rarely, blue-green hue, with the transparency decreasing accordingly to the point of opacity. Visible crystal surfaces have a glass-like sheen , needle-like and fibrous mineral aggregates, on the other hand, have a pearl or silk sheen.

In terms of its properties, pectolite is very similar to wollastonite and bustamite .

Modifications and varieties

Larimar

Larimar variety from the Dominican Republic

Larimar is a cobalt-containing , blue-white clouded variety of pectolite, which so far (status: 2010) could only be detected at two sites: in a converted, ultra- basic volcanic rock on the Barahona peninsula in the Dominican Republic and at "Fittà" near Soave in Italy. Larimar has nothing to do with the blue amber that also occurs on Hispaniola , which is sometimes processed in the same plants in Puerto Plata and in the same way as pectolite.

Larimar was only discovered in 1974 (legend is that the larimar was already known to the indigenous people of the island) and has been used commercially as a gemstone since the early 1980s . Compared to the white pectolite, the Larimar is harder (up to 6 on the Mohs scale) and occurs exclusively in dense, finely crystalline aggregates. The sky-blue color is based on small traces of vanadium (not on copper, as there are verifiably Cu-free larimars); there are also greenish varieties, the color of which is presumably only due to lattice errors.

Other

  • Osmelith , discovered by August Breithaupt and named for its clay smell, is a thin-stemmed to fibrous pectolite variety from Niederkirchen near Wolfstein .
  • Schizolite is a manganese-containing pectolite variety
  • Stellite is an aggregate discovered by Thomson in Kilsyth (Scotland) of star-shaped, ray-like crystals of white color and pearlescent sheen. After analyzes by Heddle and Greb, the material turned out to be identical to pectolite.

Education and Locations

Spherolithic, pink pectolite from New Jersey, USA

Pektolith either forms primarily in nepheline - syenites , or hydrothermally in columns, crevices or drusen basaltic igneous rocks. It often occurs in paragenesis with various zeolites , datolites and prehnite .

As a rather rare mineral formation, pectolite can sometimes be abundant at various sites, but overall it is not very common. So far (as of 2017) around 400 sites are known to be known. In addition to its type locality Monte Baldo, the mineral was found in Italy in several places in the Aosta Valley , Liguria , Piedmont , Trentino-Alto Adige and Veneto as well as in Val Malenco in the province of Sondrio (Lombardy) and in the municipality of Castelnuovo di Val di Cecina (Tuscany) .

In Germany, pectolite occurred in the Black Forest and at the Kaiserstuhl in Baden-Württemberg; near Gladenbach and Steinperf in Hesse; in the Sauerland in North Rhine-Westphalia as well as at Niederkirchen , Bistigart and Wolfstein in Rhineland-Palatinate.

West Paterson in Passaic County (New Jersey) in the United States of America (USA), where needle-like and spherical aggregates with a diameter of up to 18 cm were found, is worth mentioning due to the extraordinary pectolite finds. Up to 5 cm long, prismatic crystals were found on Mont Saint-Hilaire in the Canadian province of Québec .

Other locations are Australia , Brazil , China , Denmark , the Dominican Republic , Finland , France , Greece , Greenland , Ireland , Japan , Madagascar , Morocco , Mexico , New Zealand , Norway , Poland , Russia , Sweden , South Africa , Tajikistan , the Czech Republic , the United Kingdom (Great Britain) and other locations in the aforementioned countries Canada and USA.

use

Larimar as a tumbled stone
Larimar cabochon set in silver
In contrast, blue smithsonite

The pectolite itself has no direct economic importance. His variety Larimar, however due to its blue-white, cloudy appearance a very popular gemstone whose colors match the best in cabochon - cut comes into play.

Due to its rarity, Larimar is a correspondingly expensive gem stone. Occasionally, therefore, forgeries of Larimar have become known, including those made of glass and porcelain . In addition, Larimar can easily be confused with visually similar and bluish colored minerals such as light blue aragonite , calcite , hemimorphite , smithsonite and turquoise .

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c d e 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.  636 .
  2. ↑ Webmineral - Pectolite (English)
  3. ↑ a b c d e Pectolite . 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 June 9, 2017]).
  4. ↑ a b c d e Mindat - Pectolite (English)
  5. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  6. ^ Mineralienatlas : localities for Larimar
  7. ^ Franz von Kobell: Pectolite and Osmelith . In: Meeting reports of the Royal Bavarian Academy of Sciences in Munich . tape 1 , 1866, p. 296–299 ( available online at publications.badw.de [PDF; 199 kB ; accessed on June 9, 2017]).
  8. ↑ Ferdinand Zirkel: Elements of Mineralogy . Salzwasser Verlag, Paderborn 2013, ISBN 978-3-86444-776-1 ( limited preview in the Google book search).
  9. ↑ Mindat - Number of localities for pectolite
  10. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 242 .
  11. ↑ Find location list for pectolite in the Mineralienatlas and Mindat
  12. ↑ EPI - Institute for Gemstone Testing: Glass imitation for Larimar
  13. ^ Stones and minerals - Larimar forgeries