Mica is a naturally occurring mineral, based on a group of silicate minerals composed of varying amounts of aluminium, potassium, magnesium, iron and water having thin sheet-like or plate-like structure with different composition and physical properties. All Mica form flat six-sided monoclinic crystals with a remarkable cleavage in the direction of large surfaces, which permits them to be easily cleaved into optically flat films. When cleaved into thin films, they remain tough and elastic even at high temperatures.
Mica minerals make some rocks sparkle! They are often found in igneous rocks such as granite and metamorphic rocks such as schist. They sparkle because light is reflected on their flat surfaces, which are where the mineral breaks along its plane of cleavage. These minerals break so easily along their cleavage that some crystals have broken into many thin layers that look like the pages of a little book. Colonial Americans used the “pages” of large mica crystals as glass for windows.
Mica is also known as Muscovite, Biotite, Phlogopite, and Lepidolite
Muscovite, commonly known as white mica, is a member of the mica family of minerals. The mica minerals all share the property of perfect basal cleavage, which means that layers of mica can be peeled off of a mica crystal in very thin sheets. It is especially easy to peel off large numbers of paper-thin sheets from a muscovite crystal. Consequently, crystals of mica, like the one shown above, are often referred to as books of mica.”(Roger Weller) Muscovite can be found in many colours such as white, yellow, silver, green and brown.
“Biotite is also known as black mica. It can be peeled off of a large crystal in thin layers but with more difficulty than peeling muscovite (white mica). Biotite does not have economic value because it lacks the transparency and electrical insulating properties found in muscovite” (Weller). The typical black to brown colour of biotite is characteristic although it is difficult to distinguish brown biotite from dark brown Phlogopite. Biotite and Phlogopite are end members in a series that is dependent on the percentage of iron. Biotite is iron rich and Phlogopite is iron poor. Biotite also has a layered structure of iron magnesium aluminium silicate sheets weakly bonded together by layers of potassium ions. These layers make the perfect cleavage. When biotite crystals are weathered they can appear to be what we know as “fool’s Gold”, a golden yellow mineral with a nice sparkle.
Phlogopite is a rarer member of the mica group not well known even by many mineral collectors. It has and still is being mined for its heat and electrical insulation properties, which are considered superior to other micas. Phlogopite, like all other micas, has a layered structure of magnesium aluminium silicate sheets inadequately bonded together by layers of potassium ions.
These potassium ion layers produce the perfect cleavage. Phlogopite is not considered a valuable mineral specimen.
Lepidolite is a new form of mica that has only been on the market in large quantities for only a decade. This newer form of mica is a lithium ore that forms only in granitic masses that contain an ample amount of lithium. Lepidolite may be found in many different colours ranging from violet to pale pink or white and rarely grey or yellow.
Exportable Mica regardless of the type must be:
- Pure: No rust, No impurities like sands and stones, No spot or stain of mud, Very Clean
- Size: Length and Breath should be 1.5 inches or more
- Thickness: 3-20mm
- Good tensile strength
- Colour: Light green.
Mica can be used in many household products.
- It acts as a filler and extender. It provides a smoother consistency, improves workability and helps to prevent cracking.
- Also in the paint industry; ground mica is used as a pigment extender and facilitates suspension due to its lightweight anatomy. The ground mica also helps prevent shrink