THE MINERAL ZINNWALDITE

  • Chemistry: K Li Fe Al (AlSi3 ) O10 (OH, F)2, Potassium lithium iron aluminum silicate hydroxide fluoride.
  • Class: Silicates
  • Subclass: Phyllosilicates
  • Group: Micas
  • Uses: mineral specimens and limited use as electrical and heat insulator for industrial purposes.
  • Specimens
Zinnwaldite is a very rare member of the mica group and is not well known even by mineral collectors. Zinnwaldite is darker colored than typical muscovite but lighter than phlogopite or biotite The dark color and density in the three iron containing micas increase with an increase in the iron and magnesium content. Zinnwaldite is difficult to distinguish from the other micas at least by ordinary methods and lacallity and enviroment are keys to identification. It is limited to special granites and their pegmatites. Zinnwaldite, like other micas, has a layered structure of lithium iron aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage. Zinnwaldite is rarely available to collectors but some nice specimens with apatite are now on the market showing nice tabular crystals.

PHYSICAL CHARACTERISTICS:

  • Color is pale brown to gray and even green.
  • Luster is vitreous to pearly.
  • Transparency crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include mostly tabular crystals with a prominant pinacoid termination. Zinnwaldite's four prism faces and two pinacoid faces form pseudo-hexagonal crystal "books". The sides of the crystal often tend to tapper Also as lamellar or granular rock forming masses.
  • Cleavage is perfect in one direction producing thin sheets or flakes.
  • Fracture is not readily observed due to cleavage but is uneven.
  • Hardness is 2.5 - 3.
  • Specific Gravity is approximately 2.9 - 3.2+ (average to slightly above average)
  • Streak is white.
  • Associated Minerals are quartz, apatite, feldspars and tin minerals.
  • Other Characteristics: cleavage sheets are flexible and elastic, meaning they can be bent and will flex back to original shape. Thin flakes show an asterism or six rayed star when a light source is viewed through the crystal due to inclusions.
  • Notable Occurrences include Cornwall, England; Germany and San Diego, California.
  • Best Field Indicators are crystal habit, color, cleavage, elastic sheets, enviroments and associations.
ZINNWALDITE specimens:
(hover for more info)
ZINNWALDITE specimen zin-1
$ 45.00
Wt: 1.7 oz
El Paso Co., Colorado
Here on this specimen, nestled between the loving arms of a beautiful, sea-green cluster of Amazonite, lies a rare member of the Mica group known as Zinnwaldite. It can only be distinguished from Muscovite through chemical laboratory analysis, as it simply has a considerably higher percentage of iron and magnesium. It is in the standard Mica "book" form, and maybe looks a tad darker than Muscovite. Hitching a ride is a smidgen of Cleavelandite, a form of Albite Feldspar. This is the only one we have- avoid the free-for-all.
no photo
zin-1 ($ 45.00)
El Paso Co., Colorado
ZINNWALDITE specimen zin-2
$ 120.00
Dims: 3.7 x 1.9 x 0.9" (9.5 x 4.8 x 2.3 cm)
Wt: 5.7 oz. (163 g)
Sentinel Rock, El Paso County, Colorado, U.S.A.
This large hand specimen consists of a "book" of Zinnwaldite mica that is in excellent condition. Its pseudohexagonal form is likewise excellent, and though its form is not complete, it is not caused by any form of damage. The book has a rather dark brown color and the standard pearly, micaceous luster, and is opaque, though individual sheets would likely be transparent. There is almost no host rock present.
no photo
zin-2 ($120.00)
Sentinel Rock, El Paso County, Colorado, U.S.A.
ZINNWALDITE specimen zin-3
$ 25.00
Dims: 1.6 x 1.4 x 1.1" (4.0 x 3.5 x 2.8 cm)
Wt: 1.2 oz. (33 g)
Londonderry, Victoria, Australia
This small hand specimen appears to consist of part of a radiating spray of highly compact Zinnwaldite blades. These blades appear to reach lengths of 1.5" (0.8 cm) and are impossible to define as individuals due to their intensely compact nature. The material strongly resembles all micas in its flaky habit and pearly luster. There is no host rock present.
no photo
zin-3 ($ 25.00)
Londonderry, Victoria, Australia
ZINNWALDITE specimen zin-4
$ 25.00
Dims: 1.2 x 0.6 x 0.1" (3.0 x 1.6 x 0.4 cm)
Wt: 1 g
Zinnwald, Erzebirge, Czech Republic
This thumbnail piece consists of a misshapen Zinnwaldite blade. The blade is in fair condition and appears to be a shard from a larger crystal. It shows no definable form, though it is definitely crystalline in nature, and has the classic brown color and pearly, micaceous luster of its specie. It is also dimly transparent. There is no host rock present, and the piece is affixed inside a plastic thumbnail box with a removable putty.
no photo
zin-4 ($ 25.00)
Zinnwald, Erzebirge, Czech Republic
ZINNWALDITE specimen zin-5
$ 100.00
Dims: 3.7 x 2.1 x 2.1" (9.4 x 5.4 x 5.3 cm)
Wt: 9.3 oz. (263 g)
Sentinel Rock, Colorado Springs, Colorado, U.S.A.
A single, large Zinnwaldite "book" extends from the albite base of this cabinet piece. The book is in excellent condition, showing little damage, and has dimensions of 1.5 x 1.2 x 0.8" (3.8 x 3.0 x 2.0 cm). It shows excellent monoclinic, pseudohexagonal form and the classic perfect cleavage. Its color is black-brown and its luster is the standard pearly. A few white microcline crystals are also embedded in the albite base.
no photo
zin-5 ($100.00)
Sentinel Rock, Colorado Springs, Colorado, U.S.A.
 

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