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Micaceous Minerals 2

Monday, 10 April 2017 08:00 AM

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.

Annite

#19645
Locality
Bigwood Township, Sudbury, Ontario, Canada 
Formula
KFe2+3(Si3Al)O10(OH)2 
Availability
Sold
Size
5 x 4 x 3 cm - Miniature 

Dark black cleavable plates to 2cm.

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

Phyllosilicate 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

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 
On Dakota Matrix
Previously Sold Annite
On Dakota Matrix
Other Available Annite
WebMineral
View Annite
Mindat
View Annite

Anthophyllite

#46713
Locality
Søndeled, Risør, Aust-Agder, Norway 
Formula
□Mg7Si8O22(OH)2 
Availability
Sold
Size
7 x 6 x 3 cm - Sm Cabinet 

A tightly compacted of bladed micaceous-like crystals to 2cm. 

Anthophyllite is 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. Bladed aggregates have perfect cleavages and are commonly lamellar with elastic fibers which resemble mica cleavages.

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


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
Polak Collection

Astrophyllite

#DP34933
Locality
Mont Saint-Hilaire, Rouville Co., Quebec, Canada 
Formula
K2NaFe2+7Ti2(Si4O12)2O2(OH)4
Availability
Sold
Size
5.5 x 3.5 x 2 cm - Sm Cabinet 

Astrophyllite is an inosilicate with a {010} perfect cleavage. This specimen shows beautiful groups of radial bronze, bladed crystals 6mm resembling a mica in Albite matrix. However, it is not phyllosilicate and thus not a mica either. It typically occurs in pegmatites, nepheline syenites and alkaline granites such as Mont Saint-Hilaire, 


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
Polak Collection

Astrophyllite

#PD39994
Locality
Langesundsfjorden, Larvik, Vestfold, Norway 
Formula
K2NaFe2+7Ti2(Si4O12)2O2(OH)4
Availability
Sold
Size
4 x 3.5 x 5 cm - Miniature 

At first glance this looks like a biotite mica. It is actually not even micaceous even though it looks micaceous. The crystals are brown, shiny, and platy, which only looks like mica but is placed in this Special Edition to show the similarity of the two minerals.


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

#PD46685
Locality
Broken Hill, New South Wales, Australia 
Availability
Available
Price
$15.00
Size
6 x 3 x 1 cm - Sm Cabinet 

A cleavable mass of dark black Biotite.

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. Rieder et. al in the Canadian Mineralogist v. 36 (1998), reclassified and placed Biotite within the Annite-Phlogopite series.

Biotite is a phyllosilicate of the Mica group. Ordinary (True or Common) Mica - with flexible cleavage plates. For more information on Mica minerals and other phyllosilicates please reference our article - Click Here.


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
Celadonite - DP34932
Celadonite - DP34932

Celadonite

#DP34932
Locality
Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada 
Formula
KMgFe3+Si4O10(OH)2 
Availability
Sold
Size
3 x 2 x 1 cm - Thumbnail 

Green fine grained Celadonite. Celadonite is a phyllosilicate and mica group member. It is an ordinary (True or Common) Mica - Dioctahderal. Mostly or ideally (?) aluminum free mica, with Mg & Fe in the (M) positions. For more information on Mica minerals and other phyllosilicates please reference our article - Click Here.

Per (Bernard and Hyrsl) usually as earthy fillings in amygdules and replacement after Augite. Very rare in minute crystals. Also as micaceous scales, widespread in formations of altered volcanic rocks on intermediate basaltic compositions and commonly associated with Montmorillonite.


Celadonite

Formula
KMgFe3+Si4O10(OH)2 
Crystal System
Monoclinic 
Crystal Habit
Earthy, Aggregates, Encrustations 
Cleavage
Perfect, None, None 
Luster
Earthy (Dull) 
Color
gray green, bluish green 
Streak
greenish white 
Class
Monoclinic - Prismatic 
Fracture
Earthy 
Hardness
Collection
Polak Collection

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