Purpurite

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Purpurite
Purpurite - Sandanab, Namibia.jpg
Purpurite from Sandanab, Namibia (size: 4.2 × 2.6 cm)
General and classification
other names

Manganese purpurite

chemical formula Mn 3+ [PO 4 ] or (Mn 3+ , Fe 3+ ) PO 4
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.AB.10 ( 8th edition : VII / A.02)
04/38/01/02
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pbnm (No. 62, position 3)Template: room group / 62.3
Lattice parameters a  = 4.78  Å ; b  = 9.77 Å; c  = 5.82 Å
Formula units Z  = 4
Physical Properties
Mohs hardness 4 to 4.5
Density (g / cm 3 ) measured: 3.2 to 3.4; calculated: 3.69
Cleavage good after {100}, imperfect after {010}
Break ; Tenacity brittle, uneven
colour reddish purple to deep dark pink, also dark brown to brownish black due to weathering
Line color light purple to light red
transparency translucent to opaque
shine Silky to matt
Crystal optics
Refractive indices n α  = 1.850 (2)
n β  = 1.860 (2)
n γ  = 1.920 (2)
Birefringence δ = 0.070
Optical character biaxial positive
Axis angle 2V = measured: 38 °; calculated: 38 °
Pleochroism X = greenish gray or gray to pinkish red; Y = Z = blood red to violet red

Purpurite is a rarely occurring mineral from the mineral class " phosphates , arsenates and vanadates ". It crystallizes in the orthorhombic crystal system with the idealized composition Mn 3+ [PO 4 ], so it is chemically a manganese phosphate . Since Purpurite forms a complete mixed crystal row with heterosite (Fe 3+ [PO 4 ]) and is therefore always found in nature with a certain amount of iron in the compound, the formula of Purpurit is generally also used with (Mn 3+ , Fe 3+ ) PO 4 indicated.

Purpurite is translucent to opaque and does not form any visible crystals. It is usually found in the form of granular to massive aggregates up to about 20 cm in size, from reddish purple to deep dark pink in color with light purple to light red streak color . The surfaces of fresh samples usually have a silky sheen . Over time, weathering can cause the color to turn from dark brown to brownish black and the surfaces become matt.

The Mohs hardness of Purpurite is between 4 and 4.5. It is therefore usually a little harder than the reference mineral fluorite (4), but softer than apatite (5) and can therefore also be scratched with a good knife.

Etymology and history

Purpurite was first discovered in the "Fair Mine" near Kings Mountain (Gaston County) in the US state of North Carolina and described in 1905 by Louis Caryl Graton and Waldemar Theodore Schaller , who named the mineral after the Latin word purpura , based on its characteristic color .

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Purpurit to general ward belonged "water clear phosphates without foreign anions " where he along with Ferrisicklerit , heterosite , Lithiophilit , Marićit , Natrophilit , Sicklerit , Simferit and triphylite the unnamed group VII / A.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 purpurite to the category of “phosphates etc. without additional anions; without H 2 O “. However, this is further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With medium-sized cations”, where it can be found together with ferrisicklerite, heterosite, lithiophilite, natrophilite, sicklerite, simferite and triphylene "Triphyline group" with the system no. 8.AB.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns purpurite to the class of "phosphates, arsenates and vanadates" and there in the department of "anhydrous phosphates etc.". Here it can only be found together with heterosite in the unnamed group 38.04.01 within the subdivision of " Anhydrous phosphates etc., A + XO 4 ".

Crystal structure

Purpurite crystallizes orthorhombically in the space group Pbnm (space group no. 62, position 3) with the lattice parameters a  = 4.78  Å ; b  = 9.77 Å and c  = 5.82 Å and 4 formula units per unit cell . Template: room group / 62.3

Education and Locations

Purpurite (size: 2.5 cm) on quartz from the Brown Thurston prospect, Rumford , Oxford County , Maine, USA

Purpurite forms mainly secondary as a crust-forming oxidation product from triphylene (LiFe [PO 3 ]) or lithiophilite (LiMn [PO 3 ]). It can rarely also arise primarily in the form of granular masses in granitic pegmatites . Various, mostly secondary phosphate minerals such as sicklerite occur as accompanying minerals .

As a rare mineral formation, purpurite could only be proven in a few sites. around 80 sites are known to date (as of 2011). In addition to its "Fair Mine" type locality , the mineral occurred in the United States, among others, in several places in Arizona , California , Colorado , Connecticut , Maine and South Dakota as well as in the "Foote Mine" (Cleveland County) and also in North Carolina in the "Animikie Red Ace" pegmatites at Fern in Wisconsin .

In Germany, purpurite has so far occurred in the pegmatite deposits near Zwiesel in the Bavarian Forest and near Hagendorf ( Waidhaus ) in the Upper Palatinate Forest.

In Austria, the mineral was found in a test spodumene mining on the ridge of fire in Carinthia (see also Mining in Carinthia ).

Other locations are among others in Australia , Brazil , China , Finland , France , Canada , Madagascar , Namibia , Portugal , Rwanda , Sweden , Spain , South Africa , the Czech Republic .

Use as a gem stone

Purpurit is due to its low hardness rather rare gemstones processed, but mostly as a tumbled stone , sometimes in a cabochon cut.

See also

literature

  • LC Graton, WT Schaller: Purpurite, a new mineral (translated from: American Journal of Science , 4th. Series: 20: pp. 146–151.) In: M. Bauer, E. Koken, Th. Liebisch (eds.) : New Yearbook of Mineralogy, Geology and Paleontology. Schweizerbart'sche Buchhandlung, Stuttgart 1906, p. 172 ff. ( Textarchiv - Internet Archive ).
  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 156 ( Dörfler Natur ).
  • 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. 240 .

Web links

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

Individual evidence

  1. ↑ 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.  427 .
  2. ↑ a b IMA / CNMNC List of Mineral Names - Purpurite (PDF 1.8 MB)
  3. ↑ Webmineral - Purpurite
  4. ↑ a b c d Purpurite , in: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF 63.2 kB )
  5. ↑ a b c d e Mindat - Purpurite
  6. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  623 (first edition: 1891).
  7. ↑ Mindat - Number of localities for purpurite