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Micaceous Minerals 3

Sunday, 19 February 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
Roscoelite - 46481
Roscoelite - 46481

Roscoelite

#46481
Locality
Srednyaya Padma mine, Zaonezhie pen., Karelia, Russia 
Formula
KV3+2(Si3Al)O10(OH)2 
Availability
Sold
Size
3.5 x 2 x 2 cm - Miniature 
Special Info
XRD Confirmed 
Special Info
EDS Confirmed 

A vanadium mica identified by Dr. Igor Pekov. Very fine grained micaceous.


Roscoelite

Formula
KV3+2(Si3Al)O10(OH)2 
Crystal System
Monoclinic 
Crystal Habit
Micaceous, Scaly, Massive 
Cleavage
Perfect, None, None 
Luster
Pearly 
Color
brown green, greenish brown, yellow green, dark brown, dark green 
Streak
greenish white 
Class
Monoclinic - Prismatic 
Hardness
2.5 
Special Info
XRD Confirmed
Special Info
EDS Confirmed
SOLD
Roscoelite - PD46684
Roscoelite - PD46684

Roscoelite

#PD46684
Locality
Stuckslager mine, El Dorado Co., California, United States 
Formula
KV3+2(Si3Al)O10(OH)2 
Availability
Sold
Size
6 x 5 x 2.5 cm - Sm Cabinet 
Tagged
vanadium  
Special Info
Type Locality 

Fine grained, tiny blackish crystals less than 0.5mm in granular rock. Roscoelite is a vanadium bearing mica.


Roscoelite

Formula
KV3+2(Si3Al)O10(OH)2 
Crystal System
Monoclinic 
Crystal Habit
Micaceous, Scaly, Massive 
Cleavage
Perfect, None, None 
Luster
Pearly 
Color
brown green, greenish brown, yellow green, dark brown, dark green 
Streak
greenish white 
Class
Monoclinic - Prismatic 
Hardness
2.5 
Collection
Phillips Collection
Special Info
Type Locality
SOLD
Sepiolite - DP46709
Sepiolite - DP46709

Sepiolite

#DP46709
Locality
Obira mine, Ono-gun, Oita prefecture, Kyushu Region, Japan 
Formula
Mg4Si6O15(OH)2·6H2
Availability
Sold
Size
8 x 4 x 1 cm - Sm Cabinet 

Sepiolite is not a mica, however is classified as a phyllosilicate stuctured with rings of tetrahedra held together by octahedral nets. It does not show micaceous habits but can be confused with a mica by its fibrous habit referred to a "mountain leather".


Sepiolite

Formula
Mg4Si6O15(OH)2·6H2
Crystal System
Orthorhombic 
Crystal Habit
Earthy, Fibrous 
Cleavage
Perfect, None, None 
Luster
Earthy (Dull) 
Color
grayish white, yellowish white, bluish green white, reddish white, gray 
Streak
white 
Class
Orthorhombic - Dipyramidal 
Fracture
Conchoidal 
Hardness
Collection
Polak Collection
Mineralpedia
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On Dakota Matrix
Previously Sold Sepiolite
On Dakota Matrix
Other Available Sepiolite
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Talc

var. steatite - #PD30884
Locality
Church Cove, Lizard Peninsula, Cornwall, Englad 
Formula
Mg3Si4O10(OH)2 
Availability
Sold
Size
11 x 4 x 2 cm - Cabinet 

Soft, tightly packed fibrous greyish green mass. The variety steatite is a low-grade talc with impurities but generally still has the greasy feeling of Talc.

Talc is a phyllosilicate with perfect, easy basal cleavage and is sectile. It is not a mica group mineral and is generally not confused with micas in hand specimen. On a microscopic level, however, the mineral might be confused with micas.


Talc

Formula
Mg3Si4O10(OH)2 
Crystal System
Monoclinic 
Crystal Habit
Foliated, Scaly, Massive 
Cleavage
Perfect, None, None 
Luster
Vitreous - Pearly 
Color
pale green, white, gray white, yellowish white, brownish white 
Streak
white 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness
Collection
Phillips Collection
Mineralpedia
View Talc
On Dakota Matrix
Previously Sold Talc
On Dakota Matrix
Other Available Talc
WebMineral
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Mindat
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Zinnwaldite

#46489
Locality
Ploskaya Mt, Western Keivy Massif, Kola Peninsula, Russia 
Formula
K(Al,Fe,Li)3(Si,Al)4O10(OH)F 
Availability
Sold
Size
4.5 x 3.5 x 1.5 cm - Miniature 
Special Info
XRD Confirmed 
Special Info
EDS Confirmed 

Dark brown cleavable mass. It is positively identified by Dr. Igor Pekov.


Zinnwaldite

Formula
KLiFe++Al(AlSi3)O10(F,OH)2 
Crystal System
Monoclinic 
Crystal Habit
Pseudo Hexagonal, Micaceous, Platy 
Cleavage
Good, None, None 
Luster
Vitreous - Pearly 
Color
light brown, silvery white, gray, yellowish white, greenish white 
Streak
white 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness
3.5-4 
Special Info
XRD Confirmed
Special Info
EDS Confirmed

Zinnwaldite

#PD46690
Locality
Irelavour Lithia mine, Hensbarrow Moors, Cornwall, England 
Formula
K(Al,Fe,Li)3(Si,Al)4O10(OH)F 
Availability
Sold
Size
8 x 4 x 1.5 cm - Sm Cabinet 

A bronzy brown cleavable, micaceous mass.

Zinnwaldite is a phyllosilicate, mica group member. It is an Ordinary (True or Common) Mica - Trioctahderal. It is a lithium bearing transitional member on the Siderophyllite-Polylitionite series.


Zinnwaldite

Formula
KLiFe++Al(AlSi3)O10(F,OH)2 
Crystal System
Monoclinic 
Crystal Habit
Pseudo Hexagonal, Micaceous, Platy 
Cleavage
Good, None, None 
Luster
Vitreous - Pearly 
Color
light brown, silvery white, gray, yellowish white, greenish white 
Streak
white 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness
3.5-4 
Collection
Phillips Collection

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