Yellow Mica - XLG

Micas are an important group of minerals. They represent the classic phyllosilicate mineral and are usually the first minerals to be thought of from this subclass of the Silicates Class. Micas are significant rock forming minerals being found in all three rock types: igneous, metamorphic and sedimentary.

Item Size: X-Large 1 1/4 - 2" (30-50mm)


GENERAL INFORMATION

Mineral Class: Silicates

Mineral Species: Phyllosilicates

Mineral Group: Micas

Chemical Formula: KA_l2(AlSi₃O₁₀)(F, OH)₂ - Potassium Aluminum Silicate Hydroxide Fluoride

Composition:
09.81% - Potassium K
20.30% - Aluminum Al
21.13% - Silicon Si
00.46% - Hydrogen H
47.35% - Oxygen O
00.95% - Fluorine F

Environment: Granites and pegmatites.

IMA Status: Valid Species (Pre-IMA) 1850

Locality: Common world wide.

Name Origin: From Muscovy glass, alluding to the Russian province of Muscovy.

Aragonite Sources: India, Pakistan, Brazil and many USA localities.


PHYSICAL PROPERTIES

Cleavage: Perfect

Color: Yellow

Crystal System: Monoclinic - Prismatic

Density: 2.77 - 2.88, Average = 2.82

Diaphaniety: Transparent to translucent

Fracture: Brittle - Sectile - Brittle fracture with slightly sectile shavings possible.

Habit: Foliated - Two dimensional platy forms.

Habit: Massive - Lamellar - Distinctly foliated fine-grained forms.

Habit: Micaceous - Platy texture with "flexible" plates.

Hardness: 2-2.5 - Gypsum-Finger Nail

Luminescence: None

Luster: Vitreous (Glassy)

Magnetism: Nonmagnetic

Specific Gravity: ~2.80

Streak: White

Because thin flakes of mica are generally flexible and brittle, it is surprising how resistant and durable mica crystals can be in withstanding high temperatures and pressures in metamorphic regimes as well as the punishment of erosional environments.

The term "mica" is so familiar to the general public that it is often considered a mineral in itself. Of course it is actually a group of minerals and most people who are knowledgeable about minerals know the three most common mica minerals: muscovite, biotite, and lepidolite and perhaps a few of the less common micas glauconite, paragonite, phlogopite and zinnwaldite.

The Mica Group is actually a rather large group of minerals with over 30 members.