What is the formula for plagioclase?
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What is the formula for plagioclase?
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group….
| Plagioclase | |
|---|---|
| Formula (repeating unit) | NaAlSi3O8 – CaAl2Si2O8 |
| IMA symbol | Pl |
| Crystal system | Triclinic |
| Crystal class | Pinacoidal (1) (same H-M symbol) |
What are the end member formulas of the plagioclase feldspar series?
Albite (NaAlSi3O8—usually designated Ab) and anorthite (CaAl2Si2O8—An) are end-members of the plagioclase series. Sanidine, anorthoclase, and the perthites are alkali feldspars whose chemical compositions lie between Or and Ab.
What is the formula of albite?
| Mineral name | Chemical Formula |
|---|---|
| albite | NaAlSi3O8 |
| forsterite | Mg2SiO4 |
| diopside | CaMgSi2O6 |
| hematite | Fe2O3 |
What is the streak of plagioclase?
Plagioclase Feldspar Physical Properties
| Color | Usually white or gray. Also colorless, yellow, orange, pink, red, brown, black, blue, green. |
|---|---|
| Streak | White |
| Luster | Vitreous. Pearly on some cleavage faces. |
| Cleavage | Perfect in two directions that intersect at approximately 90 degrees. |
| Diaphaneity | Translucent to transparent |
What is plagioclase made of?
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 is plagioclase feldspar structure?
| Physical Properties of Plagioclase | |
|---|---|
| Chemical Classification | Silicate |
| Diagnostic Properties | Perfect cleavage, with cleavage faces intersecting at right angles and striations often present on cleavage faces. Well-defined crystals are extremely rare. |
| Chemical Composition | NaAlSi3O8 – CaAl2Si2O8 |
| Crystal System | Triclinic |
What are the two end members of the plagioclase series?
The Plagioclase series is a group of related feldspar minerals that essentially have the same formula but vary in their percentage of sodium and calcium. Albite and Anorthite are the end members of the series, with the intermediary minerals Oligoclase, Andesine, Labradorite, and Bytownite.
What are the formulas of feldspar?
Answer: The chemical formula of feldspar is KAlSi3O8 or NaAlSiO3 or CaAl2Si2O8. Feldspar is the most important mineral-forming rock and comprises nearly two-thirds of the igneous rocks.
Is plagioclase uniaxial or biaxial?
Two cleavages, but cleavage is often not well developed. Interference figure – biaxial (- or +), large 2V. Plagioclase may be confused with quartz, but quartz lacks cleavage, lacks twinning, does not alter, exhibits undulatory extinction, and is uniaxial.
What type of mineral is plagioclase?
Where is plagioclase formed?
Oligoclase, the most common plagioclase, occurs in granite, diorite, and other felsic igneous rocks and in some metamorphic rocks; notable occurrences are at Aust-Agder, Norway, and Fine, New York, United States.
What is the feldspar formula?
The chemical formula of feldspar is KAlSi3O8 or NaAlSiO3 or CaAl2Si2O8. Feldspar is the most important mineral-forming rock and comprises nearly two-thirds of the igneous rocks.
What type of silicate is plagioclase?
How many cleavage directions does plagioclase have?
Physical Properties of Plagioclase Minerals All feldspar minerals have two directions of perfect cleavage. 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.
What is the chemical composition of plagioclase feldspar?
| Physical Properties of Plagioclase | |
|---|---|
| Chemical Classification | Silicate |
| Specific Gravity | 2.6 to 2.8 |
| Diagnostic Properties | Perfect cleavage, with cleavage faces intersecting at right angles and striations often present on cleavage faces. Well-defined crystals are extremely rare. |
| Chemical Composition | NaAlSi3O8 – CaAl2Si2O8 |
