What are the optical properties of feldspar?
Mineral Group: Feldspar group, plagioclase series….Anorthite Optical Properties.
| Color / Pleochroism | White, grayish, reddish; colorless in thin section |
|---|---|
| 2V: | Measured: 78° to 83°, Calculated: 78° |
| RI values: | nα = 1.573 – 1.577 nβ = 1.580 – 1.585 nγ = 1.585 – 1.590 |
| Optic Sign | Biaxial (-) |
| Birefringence | δ = 0.012 – 0.013 |
What are the optical properties of plagioclase?
| Plagioclase | |
|---|---|
| Specific gravity | 2.62 (albite) to 2.76 (anorthite) |
| Optical properties | Biaxial (+) albite, biaxial (-) anorthite |
| Refractive index | Albite: nα 1.527, nβ 1.532 nγ 1.538 Anorthite: nα 1.577 nβ 1.585 nγ 1.590 |
| Solubility | Albite insoluble in HCl, anorthite decomposed by HCl |
Does feldspar have any special properties?
Most feldspar minerals have a Mohs hardness of approximately 6 to 6.5 and a specific gravity between 2.5 and 2.8. They all have a vitreous luster that is often pearly on cleavage faces.
What is the streak of feldspar?
Feldspars have a hardness of 6, have a smooth, glassy or pearly luster, and show good cleavages along two planes at nearly right angles to each other. Specific gravity is about 2.6. The streak is white, but the color of the mineral is highly variable.
Can feldspar be translucent?
Plagioclase has a color range from white to dark gray, and it’s typically translucent. Alkali feldspar (also called potassium feldspar or K-feldspar) has a color range from white to brick-red, and it’s typically opaque.
What is the transparency of feldspar?
As a group, feldspars range from transparent to nearly opaque, have nonmetallic lustres—typically vitreous to subvitreous on fractures and pearly or porcelaneous on cleavage surfaces, exhibit two cleavages—one perfect, the other good—at or near 90° to each other, and have a Mohs hardness of approximately 6.
Why is feldspar used in glass?
Glass: Feldspar is an important ingredient in the manufacture of glass and an important raw material as well, because it acts as a fluxing agent, reducing the melting temperature of quartz and helping to control the viscosity of glass.
What is the streak color of feldspar?
white
Feldspars have a hardness of 6, have a smooth, glassy or pearly luster, and show good cleavages along two planes at nearly right angles to each other. Specific gravity is about 2.6. The streak is white, but the color of the mineral is highly variable.
What color is alkali feldspar?
Alkali feldspar (also called potassium feldspar or K-feldspar) has a color range from white to brick-red, and it’s typically opaque. Many rocks have both feldspars, like granite.
Is feldspar see through?
Sanidine is usually distinguished rather easily from the other alkali feldspars because it typically appears glassy—i.e., it tends to be colourless, and much of it is transparent. Microcline and orthoclase, by contrast, are characteristically white, light gray, or flesh- to salmon-coloured and subtranslucent.
How is alkali feldspar formed?
It is usually formed by recrystallization of feldspar, and sometimes by direct crystallization from magma and hydrothermal processes. Microcline typically displays albite and pericline twining show fine parallel twin laminae typically found in the alkali feldspars microcline.
Which elements are components of alkali feldspar?
alkali feldspar A group of silicate minerals that contain the alkali metal elements potassium and sodium.
What does feldspar do in a glaze?
Feldspars are used as fluxing agents to form a glassy phase at low temperatures and as a source of alkalies and alumina in glazes. They improve the strength, toughness, and durability of the ceramic body, and cement the crystalline phase of other ingredients, softening, melting and wetting other batch constituents.
Does feldspar have a glassy luster?