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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.

SOLD
Ferroceladonite - 46456
Ferroceladonite - 46456

Ferroceladonite

#46456
Locality
Mikhailovskoe iron deposit, Kursk Oblast, Russia 
Formula
KFe2+Fe3+Si4O10(OH)2 
Availability
Sold
Size
4 x 1.5 x 0.6 cm - Miniature 
Special Info
XRD Confirmed 
Special Info
EDS Confirmed 

Green fine micaceous crystals less than 0.1mm throughout matrix. Identified by Dr. Igor Pekov.


Ferroceladonite

Formula
KFe2+Fe3+Si4O10(OH)2 
Crystal System
Monoclinic 
Crystal Habit
Microscopic Crystals 
Cleavage
Perfect, None, None 
Luster
Earthy (Dull) 
Color
dark bluish green 
Streak
paler green 
Class
Monoclinic - Prismatic 
Fracture
Earthy 
Hardness
2-2.5 
Special Info
XRD Confirmed
Special Info
EDS Confirmed
SOLD
Fluorannite - 46458
Fluorannite - 46458

Fluorannite

in cryolite - #46458
Locality
Katugin Nb-REE deposit, Siberia, Russia 
Formula
KFe2+3(Si3Al)O10F2 
Availability
Sold
Size
3 x 2 x 1 cm - Thumbnail 

Fluorannite is the fluorine analogue of Annite. It is basically compact black and micaceous. It is actualy quite rare having been found in only three worldwide localities thus far.


Fluorannite

Formula
KFe2+3(Si3Al)O10F2 
Crystal System
Monoclinic 
Crystal Habit
Foliated, Fibrous, Tabular 
Cleavage
Perfect, None, None 
Luster
Sub Metallic 
Color
iron black 
Streak
gray 
Class
Monoclinic - Prismatic 
Fracture
Sectile 
Hardness

Lepidolite

var. ball-peen - #37795
Locality
Bennett quarry, Buckfield, Oxford Co., Maine, United States 
Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Availability
Sold
Size
11 x 7 x 4 cm - Cabinet 

Lilac "Lepidolite" forming rounded crystals. Lepidolite is a lithium rich mica falling withing the solid solution of polylithionite - trilithionite. According to Dr. David London, the lilac or purple color is not due to the presence of lithium but due to the presence of minor manganese. Lepidolite is found chiefly in pegmaties but not exclusive to pegmatites.

"Lepidolite" was actually discredited as a unique mineral species. It is rather a "catch-all" name describing purple or lilac colored Muscovites belonging to the solid solution group of Polylithionite - Trilithionite, which are lithium rich micas. Lepidolite is often found in LCT (lithium - cesium - tantalum) pegmatites and can often be enriched in rubidium.

This particular habit of Lepidolite is often described as "ball-peen" Lepidolite for its similarity to the ball-peen hammer. David London describes this habit in his book "Pegmatites" and again sites differential or rapid growth in the constantly evolving chemical environment. 


Lepidolite

Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Crystal System
Monoclinic 
Crystal Habit
Platy, Foliated, Massive 
Cleavage
Perfect, None, None 
Luster
Vitreous - Pearly 
Color
colorless, gray white, lilac, yellowish, white 
Streak
white 
Class
Monoclinic 
Fracture
Uneven 
Hardness
2.5-3 
Collection
Art Smith Collection

Lepidolite

#39884
Locality
Minas Gerais, Brazil 
Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Availability
Sold
Size
8 x 5 x 3 cm - Sm Cabinet 
Tagged
pegmatite mineral  

This specimen is a rich purple cleavable mass of the lithium rich mica, which actually falls within the  Polylithionite-Trilithionite series.


Lepidolite

Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Crystal System
Monoclinic 
Crystal Habit
Platy, Foliated, Massive 
Cleavage
Perfect, None, None 
Luster
Vitreous - Pearly 
Color
colorless, gray white, lilac, yellowish, white 
Streak
white 
Class
Monoclinic 
Fracture
Uneven 
Hardness
2.5-3 
Collection
McConlogue Collection

Lepidolite

#43753
Locality
Taquaral, Itinga, Minas Gerais, Brazil 
Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Availability
Sold
Size
7.5 x 7.5 x 3 cm - Sm Cabinet 

Purple "ball-peen" Lepidolite.


Lepidolite

Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Crystal System
Monoclinic 
Crystal Habit
Platy, Foliated, Massive 
Cleavage
Perfect, None, None 
Luster
Vitreous - Pearly 
Color
colorless, gray white, lilac, yellowish, white 
Streak
white 
Class
Monoclinic 
Fracture
Uneven 
Hardness
2.5-3 

Margarite

#BM41816
Locality
Chester Emery mines, Hampden Co., Massachusetts, United States 
Formula
CaAl2(Si2Al2)O10(OH)2 
Availability
Sold
Size
9.5 x 5 x 5 cm - Cabinet 

Pinkish grey micaceous Margarite from this classic locality.

Margarite is a phyllosilicate - and  a mica group member. It is defined as dioctahedral brittle mica. Aluminum occupies the (M) octahedral positions with possible subsitutes of lithium, calcium (or possibly Na) at the Interlayer spots, and hydroxyl at the (A) positions. Be and Al can replace Si at the (T) positions. For more information on Mica minerals and other phyllosilicates please reference our article - Click Here.

Margarite occurs rarely as good pseudohexagonal crystals, usually scaly or platy aggregates as is this specimen. Grayish pink to pink, but also yellowish. Occurs mainly with diaspore in contact metamorphic deposits (Bernard & Hrysl), also in chlorite schists (Mindat). Associated with corundum, diaspore, tourmaline, staurolite, glauphane, chlorite, and magnetite...in high aluminun deposits (Handbook of Min.).


Margarite

Formula
CaAl2(Si2Al2)O10(OH)2 
Crystal System
Monoclinic 
Crystal Habit
Lamellar, Massive - Lamellar, Scaly 
Cleavage
Good, None, None 
Luster
Pearly 
Color
white, gray, pinkish gray, yellowish gray 
Streak
white 
Class
Monoclinic - Prismatic 
Fracture
Brittle 
Hardness
Collection
McConlogue Collection
Mineralpedia
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On Dakota Matrix
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Mindat
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