Mica ( Fuchsite , Muscovite , Lepidolite )

The mica group includes several closely related minerals having nearly perfect basal cleavage.

All are monoclinic with tendency towards pseudohexagonal crystals.

Mica is a group related aluminum silicate minerals that are soft and have perfeact basal cleavage.

Classification

X2Y4-6Z8O20(OH, F)4

in which

X is K, Na, or Ca and less commonly Ba, Rb or Cs

Y is Al, Mg or Fe and less commonly Mn, Cr, Ti, Li etc

Z is Si or Al but can include Fe or Ti

Micas can be classed as dioctahedral Y=4 and trioctahedral Y=6

If the X ion is K or Na, the mica is common mica and if the X ion is Ca, the mica is brittle mica.

Characteristics of all Micas:

Crystal form: monoclinic

Very solubile in water

Clasification:

Dioctahedral micas

Muscovite

Trioctahedral micas

Common micas:

Biotite

Lepidolite (lithium, rubidium and caesium mica)

Phlogopite

Zinnwaldite

Brittle micas:

Clintonite

Others:

Fuchsite (chromium mica)

Uses:

The crystalline structure of mica forms layers that can be split or delaminated into thin sheets usually causing foliation in rocks.

These sheets are chemically inert, dielectric, elastic, flexible, hydrophilic, insulating, lightwheight, platy, reflective, refractive, resilient and range in opacity from transparent to opaque.

Mica is stable when exposed to electricity, light, moisture and extreme temperature.

Is a superior electrical isulator and dielectric and can support electrostatic field while dissipating minimal energy in form of heat.

IT can be split very thin 0,025-0,125 mm or thinner; while maintaining its electrical properties.

Has high dielectric breakdown, is thermally stable to 500 Celsius and is resistant to corona discharge.

Muscovite is principal used in electrical industry, in capacitors, ideal for high frequency and radio frequency.
Phlogopite mica remains stable at higher then 900 Celsius and is used in high heat stability and electrical properties.

Minerals from Mica group, varieties:

Fuchsite (chromium mica), also known as chrome mica is a chromium Cr rich variety of muscovite from mica group of phyllosilicates minerals with formula K(Al,Cr)2(AlSi3O10)(OH)2

Trivalent chromium replaces one of the aluminium Al atoms in the general muscovite formula producing apple green fuchsite.

Color common green to emerald green depending of Cr substitution

Hardness 2-2,5 Mohs

Fuchsite has a lime green fluorescence under long wave UV light

Fuchsite radioactivity is due to its potassium content but is barely detectable.

Luminescence: triboluminescence
Common associates: Quartz, Rutile, Pyrite, Kyanite, Ruby, Glaucophane, Corundum, Phlogopite, Gold

Ruby can be found in Fuchsite but also in Zoisite; Zoisite being harder with 6 to 7 on Mohs scale

Fuchsite from Austria

Ruby in fuchsite matrix from India:

Verdite is a type of metamorphic rock made mostly of an impure often multicolored variety of fuchsite, used for ornamental carvings.

Muscovite is the most common form of mica, mane derived from muscovy glass, which describes thick sheets of transparent mica that were once used as glass in Russia.

Can form enormous crystals that can weigh alot.

Thin sheets can be peeled of as layers and thinner layer is peeled the greater its transparency becomes.

Except for large and resistant specimens, Muscovite is very hard to clean because if washed it will absorb water internally and start to break apart.

The best way to wash Muscovite and other Micas is with dry electric toothbrush.

Formula: KAl3Si3O10(OH)2

9,81% Potassium, 20,30% Aluminum, 21,13% Silicon, 0,46% Hydrogen, 47,35% Oxygen, 0,95% Fluorine

Composition: basic potassium aluminum silicate, sometimes with some chromium or manganese replacing the aluminium

Variable formula: K(Al, Cr, Mn)3Si3O10(OH)2

Color: colorless, white, beige, yellow, brown, gray, green, pink, purple, red, black, multicolored

Streak colorless, white

Hardness 2-2,5 Mohs

Forms thick flakes

Transparent to translucent

Specific gravity 2,7-3,0

Density: 2,77-2,88

Luster pearly

Cleavage 1,1

Fracture uneven

Tenacity sectile, elastic

Tendency to peel off

Rock type: igneous, metamorphic

Luminescence: yellowish white in long and short wave, fluorescence, phosphorescence, triboluminescence; or no luminescence at all

Star muscovite - describes twinned muscovite crystal in pointed star shaped sections

Common minerals associations: albite, quartz, microcline, almadine, spodumene, aquamarine, fluorite, fluorapatite, smoky quartz

Distinguishing similar minerals:

Chlorite and Margarite - not as elastic as muscovite

Biotite, Phlogopite - usually darker in color, otherwise very difficult to distinguish

Lepidolite - very difficult to distinguish from pink muscovite

Hypsum - cannot be peeled into micaceous sheets, crystals usually differently shaped

Lepidolite (lithium mica) - is a rich lithium mica known for pink and lilac colors.

 Most common matrix mineral to tourmaline and quartz.

Many time can be identical to muscovite, being incorrectly labeled as lepidolite.

Is it associated with other lithium bearing minerals like spodumene in pegmatite bodies.

It is one of the major sources of the rare alkali metals rubidium and caesium.

In 1861 Robert Bunsen and Gustav Kirchhoff extracted 150 Kg of lepidolite and yielded a few grams of rubidium salts for analysis and discovered the new element rubidium.

It occurs in granite pergmatites in some high temperature quartz veins, greisens and granites.

Formula K(Li,Al)3(Si,Al)4O10(F,OH)2

10,07% Potassium; 3,58% Lithium; 6,95% Aluminum; 28,93% Silicon; 0,26% Hydrogen; 45,32% Oxygen, 4,89% Fluorine

Other source (wikipedia) says formula: K(Li,Al,Rb)2(Al,Si)4O10(F,OH)2

Composition: basic potassium lithium aluminum fluoro-silicate

Color pink to purple, occasionaly light gray and yellow

Streak white

Hardness 2,5-3

Often forms scaly crystals in dense agregates, tabular, foliated, flaky and scaly forms

Transparent to translucent

Specific gravity 2,8-2,9

Density 2,8-2,9

Luster pearly

Cleavage 1,1

Fracture uneven

Tenacity sectile, elastic

Tendency to peel off

Rock type igneous

Optical properties biaxial (-)

Luminescence: fluorescence unknown; triboluminescence, thermoluminescence

Associated minerals include quartz, feldspar, spodumene, amblygonite, tourmaline, columbite, cassiterite, topaz and beryl.

Distinguishing minerals similar:

Pink muscovite - very hard to distinguish

Pink Chlorite - not found in granite pegmatites

Phlogopite - more reddish brown in color

Lepidolite from South Africa:

Other varieties:

Alurgite - manganese rich, pink to red variety of muscovite

Mariposite - green form of muscovite mica, forms in metamorphasized dolomite and quartz, usually present as veins or at the base of the mineral

Schernikite - light pink form of muscovite

Sericite - fine grained form of mica, usually muscovite with silky appearance

Binnite - posible form of muscovite rich in Barium Ba

Other names: fuchsite mica mic micka muscovite muscovit muscovitul fuchsitul fuchsit  lepidolit lepidolitul lepidolite