Piedmont

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Piedmont
Piemontite -St.Marcel, Aosta.JPG
Piedmontite crystals in the host rock from St. Marcel, Aosta , Italy
General and classification
chemical formula
  • Ca 2 (Al 2 Mn 3+ ) [O | OH | SiO 4 | Si 2 O 7 ]
  • Ca 2 (Mn 3+ , Fe) (Al, Mn 3+ ) 2 [O | OH | SiO 4 | Si 2 O 7 ]
Mineral class
(and possibly department) 		Silicates and Germanates - group silicates
System no. to Strunz
and to Dana 		9.BG.05a ( 8th edition : VIII / C.23)
58.02.01a.05
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / m (No. 11)Template: room group / 11
Lattice parameters a  = 8.87 to 8.90  Å ; b  = 5.65 to 5.67 Å; c  = 10.16 to 10.18 Å,
β  = 115.43 to 115.48 °
Formula units Z  = 2
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 3.46 to 3.54; calculated: [3.45]
Cleavage completely after {001}; indistinct after {100}
Break ; Tenacity uneven
colour reddish-brown to deep red, red-violet to almost black
Line color reddish
transparency translucent to opaque
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.725 to 1.756
n β  = 1.730 to 1.789
n γ  = 1.750 to 1.832
Birefringence δ = 0.025 to 0.076
Optical character biaxial positive
Axis angle 2V = 50 to 86 ° (measured); 54 ° to 86 ° (calculated)
Pleochroism Visible:
X = light yellow, orange to pink
Y = light to dark purple
Z = pink to deep red

Piedmontite (also piëmontite or manganese epidote ) is a rarely occurring mineral from the mineral class of " silicates and germanates " with the chemical composition Ca 2 (Al 2 Mn 3+ ) [O | OH | SiO 4 | Si 2 O 7 ] and From a chemical point of view, it is therefore a calcium - aluminum - manganese silicate with additional oxygen and hydroxide ions . Structurally, Piedmontite belongs to the group silicates .

Piedmontite crystallizes in the monoclinic crystal system and develops mostly prismatic crystals , but is also found in the form of radial to granular aggregates . The translucent to opaque crystals range in color from reddish-brown to deep red or red-violet to almost black and have a glass-like sheen on the surface .

Etymology and history

Piedmontite was first found in 1853 in Saint-Marcel / Piemont in Italy and described by Gustav Adolf Kenngott , who named the mineral after its type of locality .

classification

Already in the outdated, but partly still in use 8th edition of the mineral systematics according to Strunz , the Piedmontite belonged to the mineral class of "silicates and germanates" and there to the department of "group silicates (sorosilicates)", where together with allanite (Ce) , allanite - (La) , allanite (Nd) , allanite (Y) , dissakisite (Ce) , dissakisite (La) , dollaseite (Ce) , epidote , epidote (Pb) ( hancockite ), ferriallanite (Ce ) , Gatelite (Ce) , clinozoisite , clinozoisite (Sr) ( niigataite ), khristovite (Ce) , manganiandrosite (Ce) , manganiandrosite (La) ( androsite (La) ), tweddillite ( manganipiemontite (Sr ) ), Mukhinit , Piemontit- (Sr) ( Strontiopiemontit ) Uedait- (Ce) , Vanadoandrosit- (Ce) , Västmanlandit- (Ce) , Zoisit the " Epidotgruppe " with the system number. VIII / C.23 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), also assigns Piedmontite to the group of “group silicates”. However, this is further subdivided according to the structure of the silicate groups and the coordination of the cations involved , so that the mineral can be classified according to its structure in the subsection “Group silicates with mixed SiO 4 and Si 2 O 7 groups; Cations in octahedral [6] and greater coordination "can be found, where together with chromotawmawit (H), epidote, epidote- (Pb) (Rn), epidote- (Sr), ferriepidote (H), ferriepidote- ( Pb) (H), ferriepidot (Sr) (H), clinozoisite, clinozoisite (Pb) (H), clinozoisite (Sr) (Rn), manganipiemontite (H), tweddillite (Rn), mukhinite, mukhinite ( Pb) (H), Mukhinite- (Sr) (H), Piemontite- (Pb) (H), Piemontite- (Sr) (Rn), Vanadoepidot (H), Vanadoepidot- (Pb) (H), Vanadoepidot- ( Sr) (H) the "epidote group" with the system no. 9.BG.05a forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking area , classifies the Piedmontite in the already somewhat more finely subdivided division of "group silicates: insular, mixed, individual and larger tetrahedral groups". Here, however, it is also in the " epidote group (clinozoisite subgroup) " with the system no. 58.02.01a within the sub-section “Group Silicates : Insular, mixed, single and larger tetrahedral groups with cations in [6] and higher coordination; Single and double groups (n = 1,2) ”.

Crystal structure

Piedmontite crystallizes monoclinically in the space group P 2 1 / m (space group no. 11) with the lattice parameters a  = 8.87–8.90  Å ; b  = 5.65-5.67 Å; c  = 10.16-10.18 Å and β = 115.43-115.48 ° and two formula units per unit cell . Template: room group / 11

Education and Locations

Piedmontite is mainly formed in slate , amphibolite facies or other metamorphic rocks . It is also occasionally found in igneous rocks such as rhyolites and pegmatites . Accompanying minerals include calcite , epidote , glaucophane , orthoclase , quartz and tremolite .

So far (as of 2010) the mineral has been found at around 200 sites worldwide. In addition to its type locality Piedmont, it was also found in Italy in the regions of Aosta , Liguria , Lombardy and Tuscany .

Other sites are the Antarctic ; the Chinese provinces of Qinghai and Sichuan ; the Región de Coquimbo in Chile; Bavaria , Hesse and Schleswig-Holstein in Germany; Occitania in France; Greece ; India ; Hokkaidō , Honshū , Kyūshū and Shikoku in Japan; British Columbia and Québec in Canada; Morocco ; North Macedonia ; on the South Island of New Zealand; Oppland , Rogaland , Sogn og Fjordane , Trøndelag and Telemark in Norway; Salzburg and Tyrol in Austria; in the eastern and western regions of Siberia , northwestern Russia and the Urals in Russia; several regions of Sweden ; the cantons of Graubünden , Ticino and Valais in Switzerland; Serbia ; Spain ; Limpopo and North Cape in South Africa; Tanzania ; Turkey ; Wales in the United Kingdom (Great Britain) and in several regions of the United States of America (USA).

use

Piedmontite quartz from the Prabornaz mine near Saint-Marcel in the Aosta Valley, Italy

Except as a mineral sample, Piedmontite is of little economic importance. It is occasionally made into gemstones , but there is a risk of confusion with the red zoisite variety Thulit. Among other things, thulites from Norway rarely consist of pure thulite, but almost always consist of a mixture of thulite, piedmontite, quartz, muscovite mica, tremolite and calcite. Often the Piedmontites are so strongly interspersed with quartz that they would have to be called “Piedmontite quartz”. Piedmontite muscovite quartz with a significant amount of muscovite mica produces a noticeable “glitter effect” , similar to the oligoclase variety “sun stone”, aventurine quartz or the synthetic gold flow . In the trade this stone is often offered as so-called "red aventurine quartz".

See also

literature

  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 697 (first edition: 1891).
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 214 .
  • Mariko Nagashima, Masahide Akasaka: X-ray Rietveld and 57 Fe Mössbauer studies of epidote and piemontite on the join Ca 2 Al 2 Fe 3+ Si 3 O 12 (OH) - Ca 2 Al 2 Mn 3+ Si 3 O 12 (OH ) formed by hydrothermal synthesis . In: American Mineralogist . tape 95 , 2010, p. 1237–1246 ( rruff.info [PDF; 1.9 MB ; accessed on February 28, 2017]).

Web links

Commons : Piemontite  - Collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: March 2019. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, March 2019, accessed May 20, 2019 .
  2. ^ 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.  585 .
  3. ^ David Barthelmy: Piemontite Mineral Data. In: webmineral.com. Retrieved May 7, 2019 .
  4. ↑ a b c Mariko Nagashima, Masahide Akasaka: X-ray Rietveld and 57 Fe Mössbauer studies of epidote and piemontite on the join Ca 2 Al 2 Fe 3+ Si 3 O 12 (OH) - Ca 2 Al 2 Mn 3+ Si 3 O 12 (OH) formed by hydrothermal synthesis . In: American Mineralogist . tape 95 , 2010, p. 1240 ( available online at rruff.info [PDF; 1.9 MB ; accessed on February 28, 2017]).
  5. ↑ a b c d e f g h Piemontite . 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; 76  kB ; accessed on February 28, 2017]).
  6. ↑ a b c d e f Piemontite. In: mindat.org. Hudson Institute of Mineralogy, accessed May 7, 2019 .
  7. ↑ Adolph Kenngott: The Mohs'sche mineral system, according to the current standpoint of science . Carl Gerold & Sohn, Vienna 1853, p. 75 ( available online at rruff.info [PDF; 220 kB ; accessed on May 7, 2019]).
  8. ↑ Find location list for Piemontite at the Mineralienatlas and at Mindat
  9. ↑ New gemstones: Thulite and Piedmontite quartz from Norway. In: epigem.de. EPI Institute for Gem Testing, January 29, 2019, accessed May 7, 2019 .