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Micaceous Minerals

Saturday, 26 February 2022 08:00 AM

Introducing the "Micaceous Minerals" gallery which is part of our Special Edition galleries. This gallery contains mineral specimens for sale including lepidolite, margarite, and murmanite and more from places like Itinga, Minas Gerais, Brazil, Chester Emery mines, Hampden Co., Massachusetts, United States, and Ilimaussaq complex, Narsaq, Kitaa prov., Greenland.

Lepidolite

with Muscovite - #43759
Locality
Itinga, Minas Gerais, Brazil 
Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Availability
Sold
Size
9.5 x 4 x 1 cm - Cabinet 

White Muscovite rimmed by purple Lepidolite.

Lepidolite is a lithium rich mica falling within 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

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 
SOLD
Lepidolite - 43765
Lepidolite - 43765

Lepidolite

#43765
Locality
Itinga, Minas Gerais, Brazil 
Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Availability
Sold
Size
8.5 x 3.5 x 1.5 cm - Sm Cabinet 

Purple flat mass of 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 
SOLD
Lepidolite - 43769
Lepidolite - 43769

Lepidolite

#43769
Locality
Itinga, Minas Gerais, Brazil 
Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Availability
Sold
Size
5 x 3.5 x 2 cm - Miniature 

Purple "ball peen" habit Lepidolite.

"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 

Lepidolite

#57610
Locality
Itinga, Minas Gerais, Brazil 
Formula
K(Li,Al)3(Si,Al)4O10(F,OH)2 
Availability
Sold
Size
12.5 x 12.5 x 0.5 cm - Cabinet 

A large plate of purple Lepidolite to 12.5cm and 5mm thick. The first photo is backlit and shows the outline of the pseudohexagonal crystal form. In the last two photos the growth lines of the crystal can be seen.

Lepidolite falls within the series between Polylithionite and Trilithionite.


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

#44217
Locality
Chester Emery mines, Hampden Co., Massachusetts, United States 
Formula
CaAl2(Si2Al2)O10(OH)2 
Availability
Sold
Size
8 x 7 x 3 cm - Sm Cabinet 

Large pale pink micaceous crystals to 1.5cm sandwiched between chloritic schists. Excellent specimen.

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.

Large crystals of Margarite are rare. The mineral usually forms scaly or platy aggregates. Margarite typically occurs with diaspore in contact metamorphic deposits (Bernard & Hrysl), also in chlorite schists (Mindat). It is usually occurs associated with corundum, diaspore, tourmaline, staurolite, glauphane, chlorite, and magnetite...in high aluminum 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
Mineralpedia
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Mindat
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Murmanite

#PD32101
Locality
Ilimaussaq complex, Narsaq, Kitaa prov., Greenland 
Formula
Na2Ti2(Si2O7)O2·2H2
Availability
Sold
Size
7 x 6 x 1.5 cm - Sm Cabinet 

1mm pinkish plates of Murmanite scattered about matrix.

Murmanite is not a mica but is a sorosilicate and is triclinic and contains Nb-Ti in large platy aggregates. Rare as crystals - lilac to pinkish purple in nepheline syenites and pegmatites asccording to Bernard and Hyrsl. Murmanite looks micaceous but is not, although it does have a distinct basal cleavage.


Murmanite

Formula
Na2Ti2(Si2O7)O2·2H2
Crystal System
Triclinic 
Crystal Habit
Tabular, Massive 
Cleavage
Perfect, None, None 
Luster
Vitreous - Greasy 
Color
pink, bright pink, silvery, yellow, brown 
Streak
white 
Class
Triclinic - Pedial 
Fracture
Brittle - Uneven 
Hardness
2.5-3 
Collection
Don Phillips Collection

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