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.
Is olivine a plagioclase?
Plagioclase-Olivine Inclusions (POIs) are an abundant group of chondrule-like objects with igneous textures found in carbonaceous chondrites.
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.
Does olivine have feldspar?
Feldspars are the most abundant minerals in the Earth”s crust. They are silicate minerals and are referred to as framework silicates because the tetrahedra (of Si and Al four coordinated by oxygen) are linked together in three dimensions to make a framework….Feldspar.
| HARDNESS | 6-6.5 |
|---|---|
| SPECIFIC GRAVITY | 2.56-2.76 |
What is the fracture of plagioclase feldspar?
The luster is vitreous to pearly and the diaphaneity is transparent to translucent. The tenacity is brittle, and the fracture is uneven or conchoidal, but the fracture is rarely observed due to the strong tendency of the mineral to cleave instead.
What is the difference between plagioclase feldspar and potassium feldspar?
The feldspars are divided into two main groups: Potassium feldspar (“K-spar”) and plagioclase (“plag”). Both display two cleavages and an overlapping range of colors, but only plagioclase displays tiny grooves on one cleavage known as striations.
Is plagioclase mafic?
Common rock-forming mafic minerals include olivine, pyroxene, amphibole, biotite mica, and the plagioclase feldspars. Mafic magmas are usually produced at spreading centers, and represent material which is newly differentiated from the upper mantle.
What is the chemical formula for plagioclase?
| Plagioclase | |
|---|---|
| Formula (repeating unit) | NaAlSi3O8 – CaAl2Si2O8 |
| IMA symbol | Pl |
| Crystal system | Triclinic |
| Crystal class | Pinacoidal (1) (same H-M symbol) |
Which of the following is the general formula for plagioclase?
What is the extinction angle of plagioclase?
This rollover demonstrates the inclined extinction of Plagioclase as the microscope stage is rotated approximately 45º. The characteristic twinning of Plagioclase is also visible.
Is plagioclase mafic or felsic?
Image Descriptions
| Igneous Rocks | Felsic | Mafic |
|---|---|---|
| Quartz | 25 to 35% | 0% |
| Plagioclase feldspar | 25 to 50% | 0 to 50% |
| Biotite and/or Amphibole | 0 to 20% | 0 to 30% |
| Pyroxene | 0% | 20 to 75% |
How is plagioclase feldspar different from potassium feldspar?