Zwieselite
Current inventory: 0 gems
 

  
Zwieselite is named for its first-noted occurrence at Hühnerkobel, nearby Zwiesel and Rabenstein, Germany.

Discovered in 1841; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(Fe²⁺,Mn²⁺)₂(PO₄)F

Iron Manganese Phosphate Fluoride

Molecular Weight:

225.21 gm

Composition:

Manganese

12.20 %

Mn

15.75 %

MnO

Iron

37.20 %

Fe

47.85 %

FeO

Phosphorus

13.75 %

P

31.51 %

P₂O₅

Oxygen

28.42 %

O

Fluorine

8.44 %

F

8.44 %

F

—

 —  %

F

-O=F₂

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

PHOSPHATES

Strunz 8th Ed. ID:

7/B.03-30

Nickel-Strunz 10th Ed. ID:

8.BB.10

8 : PHOSPHATES, ARSENATES, VANADATES
B : Phosphates, etc., with additional anions, without H₂O
B : With only medium-sized cations, (OH, etc.):RO₄ about 1:1

Related to:

Triplite Group. Triplite-Zwieselite Series. The Fe2+ analogue of Triplite.

Members of Group:

Triplite Group: Triplite, Zwiesellite. The Triplite Group may be considered synonymous with Wagnerite Group.

Varieties:

None

Synonyms:

Zwiselite, ICSD 4428, PDF 21-811

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Cleavable, massive, to several cm

Twinning:

None

Physical Properties

Cleavage:

Good on {001}; fair on {010}; poor on {100} (by analogy to triplite) 

Fracture:

Irregular/Uneven to Sub-conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5

Density:

3.89 - 3.97 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Dark brown, clove-brown, yellowish brown; brownish black to black if altered

Transparency:

Translucent to Opaque

Luster:

Vitreous to Resinous

Refractive Index:

1.686 - 1.703  Biaxial ( + ) 

Birefringence:

0.017

Dispersion:

Moderate to strong; r > v

Pleochroism:

Distinct; yellow-brown to reddish brown

Occurances

Geological Setting:

A primary phosphate in complex zoned granite pegmatites.

Common Associations:

Triphylite, Huéraulite, Rockbridgeite.

Common Impurities:

Mg, Ca

Type Locality:

Birkhöhe Quarry (Birkenhöhe Quarry), Zwiesel, Lower Bavaria, Bavaria, Germany

Year Discovered:

1841

View mineral photos:

Zwieselite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Zwieselite is a rare phosphate mineral that is a member of the Triplite Group of minerals that also includes Triplite. In the Triplite-Zwieselite Series, Zwieselite is the iron rich member and Triplite is the manganese rich member. Zwieselite is most often found as translucent to opaque brown massive material frequently associated with greenish or bluish-gray Triphylite. Zwieselite is rarely found as gemmy crystals suitable for faceting.

Localities for Zwieselite: In Germany, in Bavaria, from Hühnerkobel and in the Birkhöhe pegmatite, near Zwiesel; at Hörlberg; from Döfering; and at Hagendorf. From Horní Slavkov (Schlaggenwald), Czech Republic. In the Mangualde pegmatite, near Mesquitela, Portugal. At the Tremearne pegmatite, Breage, Cornwall, England. From the Storm Mountain pegmatite, Larimer County, Colorado, USA.
 

  
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