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Micaceous Minerals

Saturday, 29 December 2012 09:00 PM

Not all micaceous looking minerals fall in the MICA group of phyllosilicate minerals. Many of the other silicates appear micaceous but are not. We'll have a look at some of these minerals and hopefully explain the difference. Take a look at our article on Mica and Other Micaceous Minerals.

SOLD
Annite - PD34677
Annite - PD34677

Annite

#PD34677
Locality
Mont Saint-Hilaire, Rouville Co., Quebec, Canada 
Formula
KFe2+3(Si3Al)O10(OH)2 
Availability
Sold
Size
3.5 x 2.5 x 0.6 cm - Miniature 

Phyllosilicate - Monoclinic - Mica group member. Ordinary (True or Common) Mica - Trioctahderal. For more information on Mica minerals and other phyllosilicates please reference our article - Click Here.

Annite is the iron rich, OH end member, of the Biotite- Phlogopite series. Common in schists, worldwide, up to 3m crystals in granites of Cape Ann near Rockport, Mass. USA, crystals up to 15cm from MSH (Bernard & Hrysl). Handbook of Mineralogy - pseudohexagonal outlines, and foliated masses, in Mg poor igneous and metamorphc rocks.

This specimen is only a small dark cleavage plate.


Annite

Formula
KFe2+3(Si3Al)O10(OH)2 
Crystal System
Monoclinic 
Cleavage
Perfect, None, None 
Luster
Sub Metallic 
Color
reddish brown, black 
Streak
brownish white 
Class
Monoclinic - Prismatic 
Hardness
2.5-3 
Collection
Phillips Collection
On Dakota Matrix
Previously Sold Annite
On Dakota Matrix
Other Available Annite
WebMineral
View Annite
Mindat
View Annite

Anthophyllite

#PD34726
Locality
Ilmen mts, Chelyabinsk, Southern Urals, Russia 
Formula
□Mg7Si8O22(OH)2 
Availability
Sold
Size
4 x 3 x 2.5 cm - Miniature 

Not a Mica, nor a phyllosilicate. Anthophyllite is a inosilicate - 2D infinite chains of silicate tetrahedra, which, morphologically resemble a phyllosilicate network. Anthophyllite occurs as bladed aggregates, much like this specimen, and on a smaller scale shows lamellar with elastic fibers and easy to mistake for a mica mineral.

Typically found in medium to high grade metamorphic amphibolites and gneisses. Associated with talc, chlorite, and micas. (Handbook of Mineralogy).

This specimen is a tight aggregate as that described above.


Anthophyllite

Formula
[box]Mg7Si8O22(OH)2 
Crystal System
Orthorhombic 
Crystal Habit
Fibrous, Lamellar, Massive 
Cleavage
Perfect, Distinct, Distinct 
Luster
Vitreous - Pearly 
Color
white, greenish gray, green, clove brown, brownish green 
Streak
gray 
Class
Orthorhombic - Dipyramidal 
Fracture
Conchoidal 
Hardness
5-6 
Collection
Phillips Collection

Astrophyllite

#PD34680
Locality
Khibiny Massif, Kola Peninsula, Russia 
Formula
K2NaFe2+7Ti2(Si4O12)2O2(OH)4
Availability
Sold
Size
4 x 2 x 0.6 cm - Miniature 

Astrophyllite is NOT a mica but is an inosilicate, which can resemble mica plates in hand specimen, as is the case. Astrophyllite has a perfect cleavage, can be split like a mica in thin sheets, but is very brittle (Ency. of Minerals). The color is much like a mica also being a bronze to orange yellow. Usually found in pegmatites of nepheline syenites, alkaline granites of MSH and Magnet Cove (typical for titanium minerals). Finest crystals come from Khibiny massif (Bernard & Jaroslav).

This is a smaller specimen but with beautiful elongated bronze crystals to 1cm.


Astrophyllite

Formula
K2NaFe2+7Ti2(Si4O12)2O2(OH)4
Crystal System
Triclinic 
Crystal Habit
Bladed, Stellate, Crystalline - Fine 
Cleavage
Perfect, None, None 
Luster
Adamantine - Pearly 
Color
brown, brownish red, bronze yellow, gold yellow 
Streak
yellowish brown 
Class
Triclinic - Pedial 
Fracture
Brittle 
Hardness
3-3.5 
Collection
Phillips Collection

Biotite

series - #PD34672
Locality
Franklin, Sussex Co., New Jersey, United States 
Availability
Sold
Size
6 x 4.5 x 4 cm - Sm Cabinet 

Phyllosilicate - Monoclinic - Mica group member. Ordinary (True or Common) Mica - Trioctahderal. For more information on Mica minerals and other phyllosilicates please reference our article - Click Here.

Biotite has historically been treated as an individual mineral species and also treated as a generic dark mica in the field for those geologist without the aid of a portable XRD, which none of us had. Rieder et. al in the Canadian Mineralogist v. 36 (1998), reclassified and placed Biotite within the Annite-Phlogopite series..

This specimen is just a nice chunk with serious dark cleavage planes.


Biotite

Formula
K(Mg,Fe++)3[AlSi3O10(OH,F)2 
Crystal System
Monoclinic 
Crystal Habit
Micaceous, Lamellar, Pseudo Hexagonal 
Cleavage
Perfect, None, None 
Luster
Vitreous - Pearly 
Color
dark brown, greenish brown, blackish brown, yellow, white 
Streak
gray 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness
2.5-3 
Collection
Phillips Collection
On Dakota Matrix
Previously Sold Biotite
On Dakota Matrix
Other Available Biotite
WebMineral
View Biotite
Mindat
View Biotite
SOLD
Biotite - PD34678
Biotite - PD34678

Biotite

series with Magnetite - #PD34678
Locality
Faraday mine, Hastings Co., Ontario, Canada 
Availability
Sold
Size
5 x 4 x 3.5 cm - Miniature 

Phyllosilicate - Monoclinic - Mica group member. Ordinary (True or Common) Mica - Trioctahderal. For more information on Mica minerals and other phyllosilicates please reference our article - Click Here.

An interesting specimen with octahedral Magnetite. Magnetite is usually fromed from the breakdown of Biotite.


Biotite

Formula
K(Mg,Fe++)3[AlSi3O10(OH,F)2 
Crystal System
Monoclinic 
Crystal Habit
Micaceous, Lamellar, Pseudo Hexagonal 
Cleavage
Perfect, None, None 
Luster
Vitreous - Pearly 
Color
dark brown, greenish brown, blackish brown, yellow, white 
Streak
gray 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness
2.5-3 
Collection
Phillips Collection
On Dakota Matrix
Previously Sold Biotite
On Dakota Matrix
Other Available Biotite
WebMineral
View Biotite
Mindat
View Biotite

Biotite

series - #PD34685
Locality
Kola Peninsula, Russia 
Availability
Available
Price
$30.00
Size
9 x 7 x 3 cm - Sm Cabinet 

Phyllosilicate - Monoclinic - Mica group member. Ordinary (True or Common) Mica - Trioctahderal. For more information on Mica minerals and other phyllosilicates please reference our article - Click Here.

Large thick, very dark, thick cleavage chunck of "Biotite". This is good for a study piece in which you can breal off many cleavage planes.


Biotite

Formula
K(Mg,Fe++)3[AlSi3O10(OH,F)2 
Crystal System
Monoclinic 
Crystal Habit
Micaceous, Lamellar, Pseudo Hexagonal 
Cleavage
Perfect, None, None 
Luster
Vitreous - Pearly 
Color
dark brown, greenish brown, blackish brown, yellow, white 
Streak
gray 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness
2.5-3 
Collection
Phillips Collection
On Dakota Matrix
Previously Sold Biotite
On Dakota Matrix
Other Available Biotite
WebMineral
View Biotite
Mindat
View Biotite

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