Does biotite have high birefringence?
Biotite has moderately high birefringence. In the XP view, the biotite interference colors range up to 2nd order red (with just a hint of 2nd order blue).
Does biotite have parallel extinction?
Biotite shows parallel extinction in cross polarized light, and has perfect cleavage in one direction. The biotite mineral shown here is exhibits bird’s eye texture during extinction, and the mineral is surrounded by quartz, muscovite, and feldspars.
How many cleavage does biotite have?
Cleavage/Fracture: Biotite has one perfect cleavage, which helps produce its thin sheets (5). Crystal Form: The crystal form is monoclinic, meaning it has three uneven axes that form a rectangular prism.
How do you find the birefringence of a mineral?
Moving along the horizontal line which corresponds to the thickness of the microcscope preparation (normally between 20µm and 30µm), the band of interference colour presented by the mineral is located, and then moving up the sloping line, which passes through this colour, we will obtain the birefringence value of the …
Does plagioclase have high relief?
High -ve relief, colour and isotropy distinctive. plagioclase crystals. Colourless and nearly isotropic distinctive.
Does biotite have a streak?
It appears greenish to brown or black, and even yellow when weathered. It can be transparent to opaque, has a vitreous to pearly luster, and a grey-white streak. When biotite crystals are found in large chunks, they are called “books” because they resemble books with pages of many sheets.
What type of mineral is biotite?
silicate mineral
Biotite, also called black mica, a silicate mineral in the common mica group. It is abundant in metamorphic rocks (both regional and contact), in pegmatites, and also in granites and other intrusive igneous rocks. For chemical formula and detailed physical properties, see mica (table).
Is biotite magnetic?
The platy morphology of biotite facilitates magnetic measurements with the applied field either in the plane of the sheets (Xe⊥ ) or perpendicular to the plane (Xe∥). Thus, biotite has both magnetic and structural two‐dimensional aspects.
Is biotite valuable?
Biotite is a common rock forming mineral, being present in at least some percentage in most igneous and both regional and contact metamorphic rocks. Biotite is rarely considered a valuable mineral specimen, but it can accompany other minerals and compliment them.
Can biotite scratch glass?
1 perfect cleavage; Dark brown-black color, faint yellow-brown streak. Olive green color; Granular; Conchoidal fracture; Hardness greater than glass (H ~ 6.5 – 7). Generally clear to white; One perfect cleavage, may show up to 3 cleavages; Easily scratched with a fingernail.
What is mineral birefringence?
Many minerals exhibit birefringence, which is a directional dependence of the speed of light through the mineral. This phenomenon is used by petrologists to identify minerals in a thin section (≤ 1 mm) where a sample illuminated by polarized light is rotated under a microscope to reveal its birefringence.
What is mineral optical properties?
Optical mineralogy is the study of minerals and rocks by measuring their optical properties. Optical mineralogy is used to identify the mineralogical composition of geological materials in order to help reveal their origin and evolution. Some of the properties and techniques used include: Refractive index.
