Donpeacorite

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Donpeacorite
General and classification
chemical formula (Mn, Mg) 2 [Si 2 O 6 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		09.DA.05 ( 8th edition : VIII / F.02)
65.01.02.03
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal 2 / m 2 / m 2 / m
Room group (no.) Pbca (No. 61)
Lattice parameters a  = 18.38  Å ; b  = 8.88 Å; c  = 5.23 Å
Formula units Z  = 8
Physical Properties
Mohs hardness 5 to 6
Density (g / cm 3 ) 3.36
Cleavage perfect after (110)
colour yellow-brown
Line color Please complete!
transparency translucent to transparent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.677 to 1.692
Birefringence δ = 0.015
Optical character biaxial negative

The mineral donpeacorite is a very rare chain silicate from the pyroxene group . It crystallizes in the orthorhombic crystal system with the idealized chemical composition (Mn, Mg) 2 [Si 2 O 6 ] or the empirically determined composition (Mn 2+ 1 − x , Mg x ) MgSi 2 O 6 , with 0.5> x ≥ 0.

The crystals, which are usually only a few millimeters in size, are prismatic or strip-shaped and form interlocking or radial-beam aggregates. Donpeacorite is yellow-brown to orange-brown, transparent to translucent and has a glass luster. The density is 3.36 g / cm 3 , the Mohs hardness is 5-6.

Etymology and history

First samples of donpeacorite were recovered by JT Johnson and W. deLorraine from the 2500 m level of the Balmant Mine No. 4 (Balmant, New York , USA ). EU Peterson, LM Anovitz and E. J Essene described donpeacorite as a new mineral in 1994 and named it after the American mineralogist Donald R. Peacor in recognition of his work on the mineralogy of manganese and pyroxenes and pyroxenoids .

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Donpeacorite belonged to the mineral class of "silicates and Germanates" and then to the Department of "chain silicates and band silicates (inosilicates)" where he collaborated with enstatite , ferrosilite and Nchwaningit the "Pyroxene group - Orthopyroxene" with the system no. VIII / F.02 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 Donpeacorite to the class of "silicates and germanates" and there in the department of "chain and band silicates (inosilicates)" a. This department is, however, further subdivided according to the type of chain formation, so that the mineral is classified according to its structure in the subdivision “Chain and band silicates with 2-periodic single chains Si 2 O 6 ; Pyroxene family "is to be found, where together with akimotoite , enstatite and ferrosilite the" orthopyroxene - enstatite group "with the system no. 9.DA.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Donpeacorite to the class of "silicates and Germanates" and there in the department of "chain silicate minerals". Here it is together with enstatite and ferrosilite in the group of "orthopyroxenes" with system no. 65.01.02 within the subsection " Chain Silicates: Simple unbranched chains, W = 1 with chains P = 2 ".

Modifications and varieties

The compound MnMgSi 2 O 6 is dimorphic and donpeacorite is the orthorhombic modification. The second known modification is the monoclinic clinopyroxene Kanoite .

Education and Locations

Donpeacorite is mainly formed in the metamorphosis of manganese-rich silicate limestones under the conditions of the upper amphiboith facies (600–700 ° C, 4–8 kbar). In such marbles it occurs together with tirodite , tourmaline , braunite , manganese-containing dolomite , apatite , and anhydrite .

The type locality is the St Joe Mine; ZCA No. 4 in Balmat, New York State, USA. Other sites are the Tatehira Mine in Kumaishi on the Oshima Peninsula , Hokkaidō , Japan and the Semail Ophiolite in Bulaydah in the Khawr Fakkan massif, Oman . In addition, donpeacorite is found in some meteorites .

Furthermore, Donpeacorite could be detected in some pre-Columbian ceramics from Nicaragua and can be used to limit the production area of ​​the artifacts.

Crystal structure

Donpeacorite crystallizes orthorhombically in the space group Pbca (space group no. 61) with the lattice parameters a  = 18.38  Å ; b  = 8.88 Å and c  = 5.23 Å ​​and 8 formula units per unit cell .

The distribution of manganese on the two octahedron positions is completely ordered with all Mn on the more distorted M2 position.

See also

Individual evidence

  1. ↑ a b c d e 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.  619 .
  2. ↑ a b c d e Petersen et al. 1984
  3. ↑ MinDat - Donpeacorit at mindat.org
  4. ^ Rubin 1997
  5. ↑ G. McCafferty et al. 2007
  6. ↑ M. Stimpfel 2005

literature

  • EU Petersen, LM Anovitz, EC Essene: Donpeacorite, (Mn, Mg) MgSi 2 O 6 , a new orthopyroxene and its proposed phase relations in the system MnSiO 3 -MgSiO 3 -FeSiO 3 . In: American Mineralogist. 1984, 69, pp. 472-480 ( PDF (1.0 MB) ).
  • M. Stimpfl: The Mn, Mg-intracrystalline exchange reaction in donpeacorite (Mn 0.54 Ca 0.03 Mg 1.43 Si 2 O 6 ) and its relation to the fractionation behavior of Mn in Fe, Mg-orthopyroxene. In: American Mineralogist. 2005, 90, pp. 155-161 ( PDF (174 kB) ).
  • JW Anthony, RA Bideaux, KW Bladh, MC Nichols: Handbook of Mineralogy: Donpeacorite. American Mineralogical Society, 2001 ( PDF (72 kB) ).
  • AE Rubin: Mineralogy of meteorite groups: An Update. In: Meteoritic & Planetary Science . 1997, 32, pp. 733-734 ( bibcode : 1997M & PS ... 32..733R ).
  • G. McCafferty, J. Logee, L. Steinbrenner: X-Ray Diffraction Analysis of Greater Nicoya Ceramics. In: La Tinaja: Newsletter for Archeological Studies. 2007, 18–2, pp. 13–17 ( PDF (279 kB) ).

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