How do we identify plagioclase feldspar?
How do we identify plagioclase feldspar?
It is usually easy to distinguish plagioclase feldspars because their two planes of cleavage intersect at 90-degree angles, and their cleavage faces often display striations. These properties make plagioclase feldspars relatively easy to identify with a hand lens in coarse-grained igneous and metamorphic rocks.
What are the characteristics of plagioclase feldspar?
Plagioclase Feldspar Physical Properties
| Color | Usually white or gray. Also colorless, yellow, orange, pink, red, brown, black, blue, green. |
|---|---|
| Luster | Vitreous. Pearly on some cleavage faces. |
| Cleavage | Perfect in two directions that intersect at approximately 90 degrees. |
| Diaphaneity | Translucent to transparent |
| Mohs Hardness | 6 to 6.5 |
What does plagioclase look like in thin section?
Brittle. Colorless in thin section. No pleochroism. White and grey are common in hand sample; albite tends to be lighter and anorthite darker.
What is the color of plagioclase?
White
| Plagioclase | |
|---|---|
| Color | White, gray, or bluish white |
| Mohs scale hardness | 6–6.5 |
| Luster | Vitreous |
| Streak | White |
What is the uses of plagioclase?
Plagioclase is used in the manufacture of glass and ceramics; the iridescent varieties peristerite and labradorite are valued as gemstones or ornamental material. The primary importance of plagioclase, however, derives from its role in rock formation.
What is the twinning of plagioclase?
If the compositions surfaces are parallel to one another, they are called polysynthetic twins. Plagioclase commonly shows this type of twinning, called the Albite Twin Law, with {010} as the twin plane. Such twinning is one of the most diagnostic features of plagioclase.
What type of mineral is plagioclase?
feldspar group
Plagioclase is a member of the feldspar group (like orthoclase) and is a framework silicate. Plagioclase consists of a solid solution between the albite and anorthite end-members, and together with quartz is the most common of the rock forming minerals.
What are the examples of plagioclase?
A common series of feldspars that contain both calcium and sodium aluminum silicates. Placiogclase minerals fall in between the categories of Albite (sodium aluminum silicate) and Anorthite (calcium aluminum silicate). Examples of plagioclase minerals are: Labradorite, and sunstones.
What do we use plagioclase for?
Plagioclase is used in the manufacture of glass and ceramics; the iridescent varieties peristerite and labradorite are valued as gemstones or ornamental material. The rarest plagioclase is bytownite, which occurs in basic igneous rocks and in stony meteorites.
What is plagioclase made of?
Plagioclase is a mixture of albite (Ab), or sodium aluminosilicate (NaAlSi3O8), and anorthite (An), or calcium aluminosilicate (CaAl2Si2O8); the two intermingle and form a continuous chemical range (called a solid-solution series) between albite and anorthite (the end-members of the series).
