Petedunnite

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Petedunnite
Petedunnite.jpg
General and classification
other names

IMA 1983-073

chemical formula CaZnSi 2 O 6
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DA.15 ( 8th edition : 8 / F.01-80)
65.1.3a.5
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  = natural: 9.82 (3); synthetic: 9.7955 (8)  Å ; b  = natural: 9.00 (1); synthetic: 8.9781 (8) Å; c  = natural: 5.27 (2); synthetic: 5.251 (6) Å
α  = 90 °; β  = natural: 105.6 (2) °; synthetic: 106.033 (7) °°; γ  = 90 °
Formula units Z  = 4
Physical Properties
Mohs hardness Please complete!
Density (g / cm 3 ) natural: 3.68; synthetic: 3.853
Cleavage {110}
colour natural: dark green, synthetic: colorless
Line color Please complete!
transparency transparent
shine Glass gloss
radioactivity -
magnetism -
Crystal optics
Refractive indices n α  = natural: 1.68 (1)
n β  = natural: 1.69 (1); synthetic: 1.72 (1)
n γ  = natural: 1.70 (1)
Birefringence δ = 0.02
Optical character biaxial positive
Axis angle 2V = 80 (10) °
Pleochroism only with natural material: pale light yellow - light green

The very boring mineral petedunnite , according to Pete J. Dunn , is a very rare chain silicate from the pyroxene group with the idealized chemical composition CaZnSi 2 O 6 .

Petedunnite crystallizes with monoclinic symmetry and forms dark green aggregates of small crystals less than a millimeter in size.

Petedunnit is formed in zinc-rich metamorphic limestones in the reaction of diopside - Hedenbergit - Johannsenite - mixed crystals with a zinc-rich fluid .

Etymology and history

As early as the 1930s, zinc-rich pyroxenes were described from the metamorphic limestones of the zinc deposit of the Franklin Mine near Franklin in Sussex County , New Jersey . Charles Palache documented finds of zinc-containing Schefferit , a manganese-containing variety of diopside and Jeffersonit , a zinc-manganese and iron-rich variety of diopside.

Over 50 years later, Pete J. Dunn discovered an unusual handpiece of zinc-rich clinopyroxene at the Franklin Mine and gave it to Eric J. Essene and Donald R. Peacor of the University of Michigan for further analysis. They confirmed the high zinc content, synthesized the Zn analog of diopside (CaZnSi 2 O 6 ) and named this new pyroxene after its discoverer Pete Dunn in recognition of his extensive work on the mineralogy of the iron-zinc deposits near Franklin (New Jersey).

classification

In the structural classification of the International Mineralogical Association (IMA) Petedunnit belongs together with pyroxene , Burnettit , Davisit , diopside , Esseneit , Grossmanit , Hedenbergit , Johannsenite , Kushiroit and Tissintit to Kalziumpyroxenen (Ca pyroxene) in pyroxene .

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and has so far been used by the IMA, also assigns the Petedunnit to the class of “silicates and germanates” and there to the “chain and band silicates (inosilicates)”. This section is further subdivided according to the type of chain formation, so that the mineral is classified according to its structure in the sub-section “Chain and band silicates with 2-periodic single chains Si2O6; Pyroxene family "is to be found, where together with augite, diopside, essenite, hedenbergite and johannsenite the" Ca-clinopyroxene, diopside group "with the system no. 9.DA.15 forms.

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

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Petedunnit to the class of "silicates and Germanates" and there in the department of "chain silicate minerals". Here it is together with diopside, hedenbergite, augite, johannsenite, essenite and davisite in the group of " C 2 / c clinopyroxene (Ca-clinopyroxene)" with system no. 65.01.03a can be found in the subsection " Chain Silicates: Simple unbranched chains, W = 1 with chains P = 2 ".

Chemism

Petedunnite with the idealized composition [M2] Ca [M1] Zn [T] Si 2 O 6 is the zinc analog of diopside ( [M2] Ca [M1] Mg [T] Si 2 O 6 ), where [M2], [M1] and [T] are the positions in the pyroxene structure.

The composition of Petedunnit from the type locality is

  • [M2] (Ca 0.92 Na 0.06 Mn 2+ 0.02 ) [M1] (Zn 0.37 Mn 2+ 0.18 Fe 2+ 0.19 Fe 3+ 0.12 Mg 0.14 ) [T] (Si 1.94 Al 0.06 ) O 6

and is just in the composition area of ​​petedunnit.

The deviations from the ideal composition are essentially due to the following rows of mixed crystals . On the one hand, Zn 2+ on the [M1] positions is replaced by Mn 2+ , Fe 2+ and Mg 2+ , according to the exchange reactions

on the other hand, Zn 2+ is replaced by coupled substitutions by Fe 3+

  • [M2] Ca 2+ + [M1] Zn 2+ = [M2] Na + + [M1] Fe 3+ ( Aegirin )
  • [M1] Zn 2+ + [T] Si 4+ = [M1] Fe 3+ + [T] Al 3+ ( Esseneit )

Crystal structure

Petedunnite crystallizes with monoclinic symmetry in the space group C 2 / c (space group no. 15) with 4 formula units per unit cell . The natural mixed crystal from the type locality has the lattice parameters a  = 9.82  Å , b  = 9.00 Å, c  = 5.27 Å and β = 105.6 °. The lattice parameters of the synthetic end  link are a = 9.7955 Å, b  = 8.9781 Å, c  = 5.251 Å and β = 106.033 ° Template: room group / 15

The structure is that of clinopyroxene. Silicon (Si 4+ ) occupies the T position, which is tetrahedrally surrounded by 4 oxygen ions, calcium (Ca 2+ ) occupies the M2 position, which is octahedrally surrounded by 6 oxygen ions, and zinc (Zn 2+ ) also occupies the octahedrally coordinated M1 position. This M1 octahedron is severely distorted and zinc forms four short (strong) and 2 longer (weak) bonds to the surrounding oxygen ions. This corresponds to the strong preference of Zn 2+ for a tetrahedral environment with 4 anions.

Education and Locations

Petedunnite (green, fine-grained aggregates) and unidentified mineral of the apatite group (possibly johnbaumite ) from Franklin (New Jersey) , USA
Size 2.5 cm × 3.5 cm × 2 cm

Pure petedunnite is stable at medium to high pressure and degrades below ~ 6-10 kbar to willemite (Zn 2 SiO 4 ), hardystonite (Ca 2 ZnSi 2 O 7 ) and quartz (SiO 2 ) or below ~ 650 ° C to zinc feldspar (CaZnSi 3 O 8 ), willemite and hardystonite. Natural clinopyroxenes formed at lower pressures contain only small amounts of zinc.

Zinc-containing pyroxene is formed in calcium silicate rocks when it reacts with zinc-rich solutions or other zinc minerals such as B. Sphalerite (ZnS), typically in skarn deposits . The contact metamorphosis that leads to the formation of skarns usually takes place close to the surface at low pressure. The zinc contents of the clinopyroxenes formed in this way are low. Only a few of these skarns were methamorphically changed at pressures above 5 kBar, which enables the formation of petedunnit-rich pyroxenes.

On the other hand, pyroxenes from non-ferrous metal slags can contain 50-60 mol% petedunnite. This shows that zinc-rich pyroxenes also crystallize at 1 bar and do not necessarily indicate high pressure during formation.

Skarne

The type locality of Petedunnit is the Franklin Mine in Franklin in Sussex County , New Jersey and was the reaction of diopside - Hedenbergit - Johannsenite - solid solutions with a zinc-rich fluid formed. It occurs together with willemite, quartz, calcite and fluoroapatite and contains inclusions of willemite, calcite, genthelvin , garnet , gahnite , albite , quartz, galena , sphalerite, titanite and allanite .

Other documented occurrences include the Nain Complex on the Labrador Peninsula in the Province of Newfoundland and Labrador , Canada and the Magnet Cove Carbonatite Complex in Hot Spring County , Arkansas , USA .

Non-ferrous metal slags

Zinc-containing clinopyroxenes are a primary component of slag from the smelting of lead , silver and zinc ores and can occur here together with willemite, hardystonite, zincite , wurtzite and franklinite .

In the core area of ​​massive slag from heaps near Pontgibaud in the Massif Central , France , Petedunnit occurs together with Gahnit and Willemit.

Web links

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

Individual evidence

  1. ^ IMA Database of Mineral Properties - Petedunnite. In: rruff.info. RRUFF Project in partnership with the IMA, accessed January 7, 2019 .
  2. ↑ a b c d e f g h i j k l m n o p q r s t u v w x Eric J. Essene, Donald R. Peacor: Petedunnite (CaZnSi 2 O 6 ), a new zinc clinopyroxene from Franklin, New Jersey, and phase equilibria for zincian pyroxenes . In: American Mineralogist . tape 72 , 1987, pp. 157–166 ( minsocam.org [PDF; 1.3 MB ; accessed on October 27, 2018]).
  3. ↑ a b c Petedunnite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 7, 2019 .
  4. ↑ a b c d Günther J. Redhammer, G. Roth: A comparison of the clinopyroxene compounds CaZnSi 2 O 6 and CaZnGe 2 O 6 . In: Acta Crystallographica . C61, 2005, p. i20 – i22 ( researchgate.net [PDF; 447 kB ; accessed on October 28, 2018]).
  5. ↑ Pete J. Dunn: Franklin and Sterling Hill, New Jersey: the world's most magnificent mineral deposits (Parts 1 to 5) . 1st edition. The Franklin-Ogdensburg Mineralogical Society, Franklin, NJ 1995, p. 1-755 .
  6. ↑ Tony Nikischer: Deceased: Pete J. Dunn. In: mindat.org. Hudson Institute of Mineralogy, accessed January 7, 2019 .
  7. ^ Charles Palache : The minerals of Franklin and Sterling Hill, Sussex County, New Jersey . In: Professional Paper . tape  180 , 1937, pp. 61–64 ( limited preview in Google Book search).
  8. ↑ Subcommite on Pyroxenes, CNMMN; Nobuo Morimoto: Nomenclature of Pyroxenes . In: The Canadian Mineralogist . tape 27 , 1989, pp. 143–156 ( mineralogicalassociation.ca [PDF; 1.6 MB ; accessed on November 11, 2018]).
  9. ↑ a b Alexandra L. Huber, Soraya Heuss-Aßbichler, Karl Thomas Fehr, Geoffrey D. Bromiley: Petedunnite (CaZnSi 2 O 6 ): Stability and phase relations in the system CaO-ZnO-SiO 2 . In: American Mineralogist . tape 97 , 2012, p. 739-749 ( rruff.info [PDF; 681 kB ; accessed on October 28, 2018]).
  10. ↑ a b Maxime Vanaeckera, Alexandr Courtin-Nomadea, Hubert Bril, Jacky Laureyns, Jean-François Lenain: Behavior of Zn-bearing phases in base metal slag from France and Poland: A mineralogical approach for environmental purposes . In: Journal of Geochemical Exploration . tape 136 , 2014, pp. 1–13 , doi : 10.1016 / j.gexplo.2013.09.001 .
  11. ^ Petedunnite with willemite, calcite, quartz and fluoroapatite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 7, 2019 .
  12. ↑ Find location list for Petedunnit in the Mineralienatlas and Mindat